diff --git a/CommonMark.xcodeproj/project.pbxproj b/CommonMark.xcodeproj/project.pbxproj
index 5dfd002..c95f937 100644
--- a/CommonMark.xcodeproj/project.pbxproj
+++ b/CommonMark.xcodeproj/project.pbxproj
@@ -3,12 +3,22 @@
    archiveVersion = "1";
    objectVersion = "46";
    objects = {
+      "CommonMark::Ccmark::ProductTarget" = {
+         isa = "PBXAggregateTarget";
+         buildConfigurationList = "OBJ_25";
+         buildPhases = (
+         );
+         dependencies = (
+         );
+         name = "Ccmark";
+         productName = "Ccmark";
+      };
       "CommonMark::CommonMark" = {
          isa = "PBXNativeTarget";
-         buildConfigurationList = "OBJ_17";
+         buildConfigurationList = "OBJ_29";
          buildPhases = (
-            "OBJ_20",
-            "OBJ_24"
+            "OBJ_32",
+            "OBJ_37"
          );
          dependencies = (
          );
@@ -22,11 +32,42 @@
          path = "CommonMark.framework";
          sourceTree = "BUILT_PRODUCTS_DIR";
       };
+      "CommonMark::CommonMarkPackageTests::ProductTarget" = {
+         isa = "PBXAggregateTarget";
+         buildConfigurationList = "OBJ_45";
+         buildPhases = (
+         );
+         dependencies = (
+            "OBJ_48"
+         );
+         name = "CommonMarkPackageTests";
+         productName = "CommonMarkPackageTests";
+      };
+      "CommonMark::CommonMarkTests" = {
+         isa = "PBXNativeTarget";
+         buildConfigurationList = "OBJ_50";
+         buildPhases = (
+            "OBJ_53",
+            "OBJ_56"
+         );
+         dependencies = (
+            "OBJ_58"
+         );
+         name = "CommonMarkTests";
+         productName = "CommonMarkTests";
+         productReference = "CommonMark::CommonMarkTests::Product";
+         productType = "com.apple.product-type.bundle.unit-test";
+      };
+      "CommonMark::CommonMarkTests::Product" = {
+         isa = "PBXFileReference";
+         path = "CommonMarkTests.xctest";
+         sourceTree = "BUILT_PRODUCTS_DIR";
+      };
       "CommonMark::SwiftPMPackageDescription" = {
          isa = "PBXNativeTarget";
-         buildConfigurationList = "OBJ_26";
+         buildConfigurationList = "OBJ_39";
          buildPhases = (
-            "OBJ_29"
+            "OBJ_42"
          );
          dependencies = (
          );
@@ -37,6 +78,7 @@
       "OBJ_1" = {
          isa = "PBXProject";
          attributes = {
+            LastSwiftMigration = "9999";
             LastUpgradeCheck = "9999";
          };
          buildConfigurationList = "OBJ_2";
@@ -47,58 +89,178 @@
             "en"
          );
          mainGroup = "OBJ_5";
-         productRefGroup = "OBJ_14";
+         productRefGroup = "OBJ_19";
          projectDirPath = ".";
          targets = (
+            "CommonMark::Ccmark::ProductTarget",
             "CommonMark::CommonMark",
-            "CommonMark::SwiftPMPackageDescription"
+            "CommonMark::SwiftPMPackageDescription",
+            "CommonMark::CommonMarkPackageTests::ProductTarget",
+            "CommonMark::CommonMarkTests"
          );
       };
       "OBJ_10" = {
+         isa = "PBXGroup";
+         children = (
+            "OBJ_11",
+            "OBJ_12",
+            "OBJ_13",
+            "OBJ_14"
+         );
+         name = "CommonMark";
+         path = "Sources/CommonMark";
+         sourceTree = "SOURCE_ROOT";
+      };
+      "OBJ_11" = {
+         isa = "PBXFileReference";
+         path = "ASTOperations.swift";
+         sourceTree = "<group>";
+      };
+      "OBJ_12" = {
          isa = "PBXFileReference";
          path = "Node.swift";
          sourceTree = "<group>";
       };
-      "OBJ_11" = {
+      "OBJ_13" = {
+         isa = "PBXFileReference";
+         path = "Reduce.swift";
+         sourceTree = "<group>";
+      };
+      "OBJ_14" = {
          isa = "PBXFileReference";
          path = "SwiftAST.swift";
          sourceTree = "<group>";
       };
-      "OBJ_12" = {
+      "OBJ_15" = {
          isa = "PBXGroup";
          children = (
+            "OBJ_16"
          );
          name = "Tests";
          path = "";
          sourceTree = "SOURCE_ROOT";
       };
-      "OBJ_13" = {
+      "OBJ_16" = {
          isa = "PBXGroup";
          children = (
+            "OBJ_17",
+            "OBJ_18"
          );
-         name = "Dependencies";
-         path = "";
+         name = "CommonMarkTests";
+         path = "Tests/CommonMarkTests";
+         sourceTree = "SOURCE_ROOT";
+      };
+      "OBJ_17" = {
+         isa = "PBXFileReference";
+         path = "CommonMarkTests.swift";
          sourceTree = "<group>";
       };
-      "OBJ_14" = {
+      "OBJ_18" = {
+         isa = "PBXFileReference";
+         path = "XCTestManifests.swift";
+         sourceTree = "<group>";
+      };
+      "OBJ_19" = {
          isa = "PBXGroup";
          children = (
+            "CommonMark::CommonMarkTests::Product",
             "CommonMark::CommonMark::Product"
          );
          name = "Products";
          path = "";
          sourceTree = "BUILT_PRODUCTS_DIR";
       };
-      "OBJ_17" = {
+      "OBJ_2" = {
          isa = "XCConfigurationList";
          buildConfigurations = (
-            "OBJ_18",
-            "OBJ_19"
+            "OBJ_3",
+            "OBJ_4"
          );
          defaultConfigurationIsVisible = "0";
          defaultConfigurationName = "Release";
       };
-      "OBJ_18" = {
+      "OBJ_22" = {
+         isa = "PBXFileReference";
+         path = "Package.pins";
+         sourceTree = "<group>";
+      };
+      "OBJ_23" = {
+         isa = "PBXFileReference";
+         path = "README.md";
+         sourceTree = "<group>";
+      };
+      "OBJ_25" = {
+         isa = "XCConfigurationList";
+         buildConfigurations = (
+            "OBJ_26",
+            "OBJ_27"
+         );
+         defaultConfigurationIsVisible = "0";
+         defaultConfigurationName = "Release";
+      };
+      "OBJ_26" = {
+         isa = "XCBuildConfiguration";
+         buildSettings = {
+         };
+         name = "Debug";
+      };
+      "OBJ_27" = {
+         isa = "XCBuildConfiguration";
+         buildSettings = {
+         };
+         name = "Release";
+      };
+      "OBJ_29" = {
+         isa = "XCConfigurationList";
+         buildConfigurations = (
+            "OBJ_30",
+            "OBJ_31"
+         );
+         defaultConfigurationIsVisible = "0";
+         defaultConfigurationName = "Release";
+      };
+      "OBJ_3" = {
+         isa = "XCBuildConfiguration";
+         buildSettings = {
+            CLANG_ENABLE_OBJC_ARC = "YES";
+            COMBINE_HIDPI_IMAGES = "YES";
+            COPY_PHASE_STRIP = "NO";
+            DEBUG_INFORMATION_FORMAT = "dwarf";
+            DYLIB_INSTALL_NAME_BASE = "@rpath";
+            ENABLE_NS_ASSERTIONS = "YES";
+            GCC_OPTIMIZATION_LEVEL = "0";
+            GCC_PREPROCESSOR_DEFINITIONS = (
+               "$(inherited)",
+               "SWIFT_PACKAGE=1",
+               "DEBUG=1"
+            );
+            MACOSX_DEPLOYMENT_TARGET = "10.10";
+            ONLY_ACTIVE_ARCH = "YES";
+            OTHER_SWIFT_FLAGS = (
+               "-DXcode"
+            );
+            PRODUCT_NAME = "$(TARGET_NAME)";
+            SDKROOT = "macosx";
+            SUPPORTED_PLATFORMS = (
+               "macosx",
+               "iphoneos",
+               "iphonesimulator",
+               "appletvos",
+               "appletvsimulator",
+               "watchos",
+               "watchsimulator"
+            );
+            SWIFT_ACTIVE_COMPILATION_CONDITIONS = (
+               "$(inherited)",
+               "SWIFT_PACKAGE",
+               "DEBUG"
+            );
+            SWIFT_OPTIMIZATION_LEVEL = "-Onone";
+            USE_HEADERMAP = "NO";
+         };
+         name = "Debug";
+      };
+      "OBJ_30" = {
          isa = "XCBuildConfiguration";
          buildSettings = {
             ENABLE_TESTABILITY = "YES";
@@ -108,25 +270,27 @@
             );
             HEADER_SEARCH_PATHS = (
                "$(inherited)",
-               "$(SRCROOT)/.build/checkouts/Ccmark.git--1076946679408688698"
+               "$(SRCROOT)/Sources/Ccmark"
             );
             INFOPLIST_FILE = "CommonMark.xcodeproj/CommonMark_Info.plist";
+            IPHONEOS_DEPLOYMENT_TARGET = "8.0";
             LD_RUNPATH_SEARCH_PATHS = (
                "$(inherited)",
                "$(TOOLCHAIN_DIR)/usr/lib/swift/macosx"
             );
+            MACOSX_DEPLOYMENT_TARGET = "10.10";
             OTHER_CFLAGS = (
                "$(inherited)",
-               "-I/usr/local/Cellar/commonmark/0.25.2/include"
+               "-I/usr/local/include"
             );
             OTHER_LDFLAGS = (
                "$(inherited)",
-               "-L/usr/local/Cellar/commonmark/0.25.2/lib",
+               "-L/usr/local/lib",
                "-lcmark"
             );
             OTHER_SWIFT_FLAGS = (
                "$(inherited)",
-               "-I/usr/local/Cellar/commonmark/0.25.2/include"
+               "-I/usr/local/include"
             );
             PRODUCT_BUNDLE_IDENTIFIER = "CommonMark";
             PRODUCT_MODULE_NAME = "$(TARGET_NAME:c99extidentifier)";
@@ -135,12 +299,14 @@
             SWIFT_ACTIVE_COMPILATION_CONDITIONS = (
                "$(inherited)"
             );
-            SWIFT_VERSION = "4.2";
+            SWIFT_VERSION = "5.0";
             TARGET_NAME = "CommonMark";
+            TVOS_DEPLOYMENT_TARGET = "9.0";
+            WATCHOS_DEPLOYMENT_TARGET = "2.0";
          };
          name = "Debug";
       };
-      "OBJ_19" = {
+      "OBJ_31" = {
          isa = "XCBuildConfiguration";
          buildSettings = {
             ENABLE_TESTABILITY = "YES";
@@ -150,25 +316,27 @@
             );
             HEADER_SEARCH_PATHS = (
                "$(inherited)",
-               "$(SRCROOT)/.build/checkouts/Ccmark.git--1076946679408688698"
+               "$(SRCROOT)/Sources/Ccmark"
             );
             INFOPLIST_FILE = "CommonMark.xcodeproj/CommonMark_Info.plist";
+            IPHONEOS_DEPLOYMENT_TARGET = "8.0";
             LD_RUNPATH_SEARCH_PATHS = (
                "$(inherited)",
                "$(TOOLCHAIN_DIR)/usr/lib/swift/macosx"
             );
+            MACOSX_DEPLOYMENT_TARGET = "10.10";
             OTHER_CFLAGS = (
                "$(inherited)",
-               "-I/usr/local/Cellar/commonmark/0.25.2/include"
+               "-I/usr/local/include"
             );
             OTHER_LDFLAGS = (
                "$(inherited)",
-               "-L/usr/local/Cellar/commonmark/0.25.2/lib",
+               "-L/usr/local/lib",
                "-lcmark"
             );
             OTHER_SWIFT_FLAGS = (
                "$(inherited)",
-               "-I/usr/local/Cellar/commonmark/0.25.2/include"
+               "-I/usr/local/include"
             );
             PRODUCT_BUNDLE_IDENTIFIER = "CommonMark";
             PRODUCT_MODULE_NAME = "$(TARGET_NAME:c99extidentifier)";
@@ -177,61 +345,96 @@
             SWIFT_ACTIVE_COMPILATION_CONDITIONS = (
                "$(inherited)"
             );
-            SWIFT_VERSION = "4.2";
+            SWIFT_VERSION = "5.0";
             TARGET_NAME = "CommonMark";
+            TVOS_DEPLOYMENT_TARGET = "9.0";
+            WATCHOS_DEPLOYMENT_TARGET = "2.0";
          };
          name = "Release";
       };
-      "OBJ_2" = {
-         isa = "XCConfigurationList";
-         buildConfigurations = (
-            "OBJ_3",
-            "OBJ_4"
-         );
-         defaultConfigurationIsVisible = "0";
-         defaultConfigurationName = "Release";
-      };
-      "OBJ_20" = {
+      "OBJ_32" = {
          isa = "PBXSourcesBuildPhase";
          files = (
-            "OBJ_21",
-            "OBJ_22",
-            "OBJ_23"
+            "OBJ_33",
+            "OBJ_34",
+            "OBJ_35",
+            "OBJ_36"
          );
       };
-      "OBJ_21" = {
+      "OBJ_33" = {
          isa = "PBXBuildFile";
-         fileRef = "OBJ_9";
+         fileRef = "OBJ_11";
       };
-      "OBJ_22" = {
+      "OBJ_34" = {
          isa = "PBXBuildFile";
-         fileRef = "OBJ_10";
+         fileRef = "OBJ_12";
       };
-      "OBJ_23" = {
+      "OBJ_35" = {
          isa = "PBXBuildFile";
-         fileRef = "OBJ_11";
+         fileRef = "OBJ_13";
       };
-      "OBJ_24" = {
+      "OBJ_36" = {
+         isa = "PBXBuildFile";
+         fileRef = "OBJ_14";
+      };
+      "OBJ_37" = {
          isa = "PBXFrameworksBuildPhase";
          files = (
          );
       };
-      "OBJ_26" = {
+      "OBJ_39" = {
          isa = "XCConfigurationList";
          buildConfigurations = (
-            "OBJ_27",
-            "OBJ_28"
+            "OBJ_40",
+            "OBJ_41"
          );
          defaultConfigurationIsVisible = "0";
          defaultConfigurationName = "Release";
       };
-      "OBJ_27" = {
+      "OBJ_4" = {
+         isa = "XCBuildConfiguration";
+         buildSettings = {
+            CLANG_ENABLE_OBJC_ARC = "YES";
+            COMBINE_HIDPI_IMAGES = "YES";
+            COPY_PHASE_STRIP = "YES";
+            DEBUG_INFORMATION_FORMAT = "dwarf-with-dsym";
+            DYLIB_INSTALL_NAME_BASE = "@rpath";
+            GCC_OPTIMIZATION_LEVEL = "s";
+            GCC_PREPROCESSOR_DEFINITIONS = (
+               "$(inherited)",
+               "SWIFT_PACKAGE=1"
+            );
+            MACOSX_DEPLOYMENT_TARGET = "10.10";
+            OTHER_SWIFT_FLAGS = (
+               "-DXcode"
+            );
+            PRODUCT_NAME = "$(TARGET_NAME)";
+            SDKROOT = "macosx";
+            SUPPORTED_PLATFORMS = (
+               "macosx",
+               "iphoneos",
+               "iphonesimulator",
+               "appletvos",
+               "appletvsimulator",
+               "watchos",
+               "watchsimulator"
+            );
+            SWIFT_ACTIVE_COMPILATION_CONDITIONS = (
+               "$(inherited)",
+               "SWIFT_PACKAGE"
+            );
+            SWIFT_OPTIMIZATION_LEVEL = "-Owholemodule";
+            USE_HEADERMAP = "NO";
+         };
+         name = "Release";
+      };
+      "OBJ_40" = {
          isa = "XCBuildConfiguration";
          buildSettings = {
             LD = "/usr/bin/true";
             OTHER_SWIFT_FLAGS = (
                "-swift-version",
-               "4.2",
+               "5",
                "-I",
                "$(TOOLCHAIN_DIR)/usr/lib/swift/pm/4_2",
                "-target",
@@ -239,17 +442,17 @@
                "-sdk",
                "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk"
             );
-            SWIFT_VERSION = "4.2";
+            SWIFT_VERSION = "5.0";
          };
          name = "Debug";
       };
-      "OBJ_28" = {
+      "OBJ_41" = {
          isa = "XCBuildConfiguration";
          buildSettings = {
             LD = "/usr/bin/true";
             OTHER_SWIFT_FLAGS = (
                "-swift-version",
-               "4.2",
+               "5",
                "-I",
                "$(TOOLCHAIN_DIR)/usr/lib/swift/pm/4_2",
                "-target",
@@ -257,102 +460,183 @@
                "-sdk",
                "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk"
             );
-            SWIFT_VERSION = "4.2";
+            SWIFT_VERSION = "5.0";
          };
          name = "Release";
       };
-      "OBJ_29" = {
+      "OBJ_42" = {
          isa = "PBXSourcesBuildPhase";
          files = (
-            "OBJ_30"
+            "OBJ_43"
          );
       };
-      "OBJ_3" = {
+      "OBJ_43" = {
+         isa = "PBXBuildFile";
+         fileRef = "OBJ_6";
+      };
+      "OBJ_45" = {
+         isa = "XCConfigurationList";
+         buildConfigurations = (
+            "OBJ_46",
+            "OBJ_47"
+         );
+         defaultConfigurationIsVisible = "0";
+         defaultConfigurationName = "Release";
+      };
+      "OBJ_46" = {
          isa = "XCBuildConfiguration";
          buildSettings = {
-            CLANG_ENABLE_OBJC_ARC = "YES";
-            COMBINE_HIDPI_IMAGES = "YES";
-            COPY_PHASE_STRIP = "NO";
-            DEBUG_INFORMATION_FORMAT = "dwarf";
-            DYLIB_INSTALL_NAME_BASE = "@rpath";
-            ENABLE_NS_ASSERTIONS = "YES";
-            GCC_OPTIMIZATION_LEVEL = "0";
-            GCC_PREPROCESSOR_DEFINITIONS = (
-               "DEBUG=1",
-               "$(inherited)"
+         };
+         name = "Debug";
+      };
+      "OBJ_47" = {
+         isa = "XCBuildConfiguration";
+         buildSettings = {
+         };
+         name = "Release";
+      };
+      "OBJ_48" = {
+         isa = "PBXTargetDependency";
+         target = "CommonMark::CommonMarkTests";
+      };
+      "OBJ_5" = {
+         isa = "PBXGroup";
+         children = (
+            "OBJ_6",
+            "OBJ_7",
+            "OBJ_15",
+            "OBJ_19",
+            "OBJ_22",
+            "OBJ_23"
+         );
+         path = "";
+         sourceTree = "<group>";
+      };
+      "OBJ_50" = {
+         isa = "XCConfigurationList";
+         buildConfigurations = (
+            "OBJ_51",
+            "OBJ_52"
+         );
+         defaultConfigurationIsVisible = "0";
+         defaultConfigurationName = "Release";
+      };
+      "OBJ_51" = {
+         isa = "XCBuildConfiguration";
+         buildSettings = {
+            CLANG_ENABLE_MODULES = "YES";
+            EMBEDDED_CONTENT_CONTAINS_SWIFT = "YES";
+            FRAMEWORK_SEARCH_PATHS = (
+               "$(inherited)",
+               "$(PLATFORM_DIR)/Developer/Library/Frameworks"
+            );
+            HEADER_SEARCH_PATHS = (
+               "$(inherited)",
+               "$(SRCROOT)/Sources/Ccmark"
+            );
+            INFOPLIST_FILE = "CommonMark.xcodeproj/CommonMarkTests_Info.plist";
+            IPHONEOS_DEPLOYMENT_TARGET = "8.0";
+            LD_RUNPATH_SEARCH_PATHS = (
+               "$(inherited)",
+               "@loader_path/../Frameworks",
+               "@loader_path/Frameworks"
             );
             MACOSX_DEPLOYMENT_TARGET = "10.10";
-            ONLY_ACTIVE_ARCH = "YES";
-            OTHER_SWIFT_FLAGS = (
-               "-DXcode"
+            OTHER_CFLAGS = (
+               "$(inherited)",
+               "-I/usr/local/include"
             );
-            PRODUCT_NAME = "$(TARGET_NAME)";
-            SDKROOT = "macosx";
-            SUPPORTED_PLATFORMS = (
-               "macosx",
-               "iphoneos",
-               "iphonesimulator",
-               "appletvos",
-               "appletvsimulator",
-               "watchos",
-               "watchsimulator"
+            OTHER_LDFLAGS = (
+               "$(inherited)",
+               "-L/usr/local/lib",
+               "-lcmark"
+            );
+            OTHER_SWIFT_FLAGS = (
+               "$(inherited)",
+               "-I/usr/local/include"
             );
             SWIFT_ACTIVE_COMPILATION_CONDITIONS = (
-               "SWIFT_PACKAGE",
-               "DEBUG"
+               "$(inherited)"
             );
-            SWIFT_OPTIMIZATION_LEVEL = "-Onone";
-            USE_HEADERMAP = "NO";
+            SWIFT_VERSION = "5.0";
+            TARGET_NAME = "CommonMarkTests";
+            TVOS_DEPLOYMENT_TARGET = "9.0";
+            WATCHOS_DEPLOYMENT_TARGET = "2.0";
          };
          name = "Debug";
       };
-      "OBJ_30" = {
-         isa = "PBXBuildFile";
-         fileRef = "OBJ_6";
-      };
-      "OBJ_4" = {
+      "OBJ_52" = {
          isa = "XCBuildConfiguration";
          buildSettings = {
-            CLANG_ENABLE_OBJC_ARC = "YES";
-            COMBINE_HIDPI_IMAGES = "YES";
-            COPY_PHASE_STRIP = "YES";
-            DEBUG_INFORMATION_FORMAT = "dwarf-with-dsym";
-            DYLIB_INSTALL_NAME_BASE = "@rpath";
-            GCC_OPTIMIZATION_LEVEL = "s";
+            CLANG_ENABLE_MODULES = "YES";
+            EMBEDDED_CONTENT_CONTAINS_SWIFT = "YES";
+            FRAMEWORK_SEARCH_PATHS = (
+               "$(inherited)",
+               "$(PLATFORM_DIR)/Developer/Library/Frameworks"
+            );
+            HEADER_SEARCH_PATHS = (
+               "$(inherited)",
+               "$(SRCROOT)/Sources/Ccmark"
+            );
+            INFOPLIST_FILE = "CommonMark.xcodeproj/CommonMarkTests_Info.plist";
+            IPHONEOS_DEPLOYMENT_TARGET = "8.0";
+            LD_RUNPATH_SEARCH_PATHS = (
+               "$(inherited)",
+               "@loader_path/../Frameworks",
+               "@loader_path/Frameworks"
+            );
             MACOSX_DEPLOYMENT_TARGET = "10.10";
-            OTHER_SWIFT_FLAGS = (
-               "-DXcode"
+            OTHER_CFLAGS = (
+               "$(inherited)",
+               "-I/usr/local/include"
             );
-            PRODUCT_NAME = "$(TARGET_NAME)";
-            SDKROOT = "macosx";
-            SUPPORTED_PLATFORMS = (
-               "macosx",
-               "iphoneos",
-               "iphonesimulator",
-               "appletvos",
-               "appletvsimulator",
-               "watchos",
-               "watchsimulator"
+            OTHER_LDFLAGS = (
+               "$(inherited)",
+               "-L/usr/local/lib",
+               "-lcmark"
+            );
+            OTHER_SWIFT_FLAGS = (
+               "$(inherited)",
+               "-I/usr/local/include"
             );
             SWIFT_ACTIVE_COMPILATION_CONDITIONS = (
-               "SWIFT_PACKAGE"
+               "$(inherited)"
             );
-            SWIFT_OPTIMIZATION_LEVEL = "-Owholemodule";
-            USE_HEADERMAP = "NO";
+            SWIFT_VERSION = "5.0";
+            TARGET_NAME = "CommonMarkTests";
+            TVOS_DEPLOYMENT_TARGET = "9.0";
+            WATCHOS_DEPLOYMENT_TARGET = "2.0";
          };
          name = "Release";
       };
-      "OBJ_5" = {
-         isa = "PBXGroup";
-         children = (
-            "OBJ_6",
-            "OBJ_7",
-            "OBJ_12",
-            "OBJ_13",
-            "OBJ_14"
+      "OBJ_53" = {
+         isa = "PBXSourcesBuildPhase";
+         files = (
+            "OBJ_54",
+            "OBJ_55"
          );
-         path = "";
-         sourceTree = "<group>";
+      };
+      "OBJ_54" = {
+         isa = "PBXBuildFile";
+         fileRef = "OBJ_17";
+      };
+      "OBJ_55" = {
+         isa = "PBXBuildFile";
+         fileRef = "OBJ_18";
+      };
+      "OBJ_56" = {
+         isa = "PBXFrameworksBuildPhase";
+         files = (
+            "OBJ_57"
+         );
+      };
+      "OBJ_57" = {
+         isa = "PBXBuildFile";
+         fileRef = "CommonMark::CommonMark::Product";
+      };
+      "OBJ_58" = {
+         isa = "PBXTargetDependency";
+         target = "CommonMark::CommonMark";
       };
       "OBJ_6" = {
          isa = "PBXFileReference";
@@ -363,7 +647,8 @@
       "OBJ_7" = {
          isa = "PBXGroup";
          children = (
-            "OBJ_8"
+            "OBJ_8",
+            "OBJ_10"
          );
          name = "Sources";
          path = "";
@@ -372,17 +657,15 @@
       "OBJ_8" = {
          isa = "PBXGroup";
          children = (
-            "OBJ_9",
-            "OBJ_10",
-            "OBJ_11"
+            "OBJ_9"
          );
-         name = "CommonMark";
-         path = "Sources/CommonMark";
+         name = "Ccmark";
+         path = "Sources/Ccmark";
          sourceTree = "SOURCE_ROOT";
       };
       "OBJ_9" = {
          isa = "PBXFileReference";
-         path = "ASTOperations.swift";
+         path = "module.modulemap";
          sourceTree = "<group>";
       };
    };
diff --git a/CommonMark.xcodeproj/xcshareddata/xcschemes/CommonMark-Package.xcscheme b/CommonMark.xcodeproj/xcshareddata/xcschemes/CommonMark-Package.xcscheme
index a26dbab..34787e8 100644
--- a/CommonMark.xcodeproj/xcshareddata/xcschemes/CommonMark-Package.xcscheme
+++ b/CommonMark.xcodeproj/xcshareddata/xcschemes/CommonMark-Package.xcscheme
@@ -28,6 +28,16 @@
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
       shouldUseLaunchSchemeArgsEnv = "YES">
       <Testables>
+         <TestableReference
+            skipped = "NO">
+            <BuildableReference
+               BuildableIdentifier = "primary"
+               BlueprintIdentifier = "CommonMark::CommonMarkTests"
+               BuildableName = "CommonMarkTests.xctest"
+               BlueprintName = "CommonMarkTests"
+               ReferencedContainer = "container:CommonMark.xcodeproj">
+            </BuildableReference>
+         </TestableReference>
       </Testables>
       <AdditionalOptions>
       </AdditionalOptions>
diff --git a/Package.resolved b/Package.resolved
deleted file mode 100644
index 8f9a492..0000000
--- a/Package.resolved
+++ /dev/null
@@ -1,16 +0,0 @@
-{
-  "object": {
-    "pins": [
-      {
-        "package": "Ccmark",
-        "repositoryURL": "https://github.com/objcio/Ccmark.git",
-        "state": {
-          "branch": "master",
-          "revision": "2d2002db33c3f077635538031008c6893a4c0ec2",
-          "version": null
-        }
-      }
-    ]
-  },
-  "version": 1
-}
diff --git a/Package.swift b/Package.swift
index a0d7ee3..529e2d9 100644
--- a/Package.swift
+++ b/Package.swift
@@ -1,16 +1,23 @@
-// swift-tools-version:4.2
+// swift-tools-version:5.5
 
 import PackageDescription
 
 let package = Package(
     name: "CommonMark",
     products: [
-        .library(name: "CommonMark", targets: ["CommonMark"])
-    ],
-    dependencies: [
-        .package(url: "https://github.com/objcio/Ccmark.git", .branch("master"))
+        .library(name: "CommonMark", targets: ["CommonMark"]),
+        .library(name: "Ccmark", targets: ["Ccmark"]),
+
     ],
+    dependencies: [],
     targets: [
-        .target(name: "CommonMark")
+        .target(name: "CommonMark", dependencies: ["Ccmark"]),
+        .systemLibrary(
+          name: "Ccmark",
+          pkgConfig: "libcmark",
+          providers: [
+            .brew(["commonmark"])
+          ]),
+        .testTarget(name: "CommonMarkTests", dependencies: ["CommonMark"]),
     ]
 )
diff --git a/Sources/Ccmark/module.modulemap b/Sources/Ccmark/module.modulemap
new file mode 100644
index 0000000..fd0db12
--- /dev/null
+++ b/Sources/Ccmark/module.modulemap
@@ -0,0 +1,5 @@
+module Ccmark [system] {
+    header "/usr/local/include/cmark.h"
+    link "libcmark"
+    export *
+}
diff --git a/Sources/CommonMark/Node.swift b/Sources/CommonMark/Node.swift
index 71abe48..1d82a8e 100644
--- a/Sources/CommonMark/Node.swift
+++ b/Sources/CommonMark/Node.swift
@@ -9,7 +9,9 @@
 import Foundation
 import Ccmark
 
-func markdownToHtml(string: String) -> String {
+
+
+func markdowntoHTML(string: String) -> String {
     let outString = cmark_markdown_to_html(string, string.utf8.count, 0)!
     defer { free(outString) }
     return String(cString: outString)
@@ -29,12 +31,49 @@ struct Markdown {
 }
 
 extension String {
-    init?(unsafeCString: UnsafePointer<Int8>!) {
+    // We're going through Data instead of using init(cstring:) because that leaks memory on Linux.
+    
+    init?(unsafeCString: UnsafePointer<CChar>!) {
         guard let cString = unsafeCString else { return nil }
-        self.init(cString: cString)
+        let data = cString.withMemoryRebound(to: UInt8.self, capacity: strlen(cString), { p in
+            return Data(UnsafeBufferPointer(start: p, count: strlen(cString)))
+        })
+        self.init(data: data, encoding: .utf8)
     }
+    
+    init?(freeingCString str: UnsafeMutablePointer<CChar>?) {
+        guard let cString = str else { return nil }
+        let data = cString.withMemoryRebound(to: UInt8.self, capacity: strlen(cString), { p in
+            return Data(UnsafeBufferPointer(start: p, count: strlen(cString)))
+        })
+        str?.deallocate()
+        self.init(data: data, encoding: .utf8)
+    }
+}
+
+/// A position in a Markdown document. Note that both `line` and `column` are 1-based.
+public struct Position {
+    public var line: Int32
+    public var column: Int32
 }
 
+public struct RenderingOptions: OptionSet {
+    public var rawValue: Int32
+    public init(rawValue: Int32 = CMARK_OPT_DEFAULT) {
+        self.rawValue = rawValue
+    }
+    
+    static public let sourcePos = RenderingOptions(rawValue: CMARK_OPT_SOURCEPOS)
+    static public let hardBreaks = RenderingOptions(rawValue: CMARK_OPT_HARDBREAKS)
+    static public let safe = RenderingOptions(rawValue: CMARK_OPT_SAFE)
+    static public let unsafe = RenderingOptions(rawValue: CMARK_OPT_UNSAFE)
+    static public let noBreaks = RenderingOptions(rawValue: CMARK_OPT_NOBREAKS)
+    static public let normalize = RenderingOptions(rawValue: CMARK_OPT_NORMALIZE)
+    static public let validateUTF8 = RenderingOptions(rawValue: CMARK_OPT_VALIDATE_UTF8)
+    static public let smart = RenderingOptions(rawValue: CMARK_OPT_SMART)
+}
+
+
 /// A node in a Markdown document.
 ///
 /// Can represent a full Markdown document (i.e. the document's root node) or
@@ -47,13 +86,14 @@ public class Node: CustomStringConvertible {
     }
     
     public init?(filename: String) {
-        guard let node = cmark_parse_file(fopen(filename, "r"), 0) else { return nil }
+        guard let file = fopen(filename, "r"),
+            let node = cmark_parse_file(file, 0) else { return nil }
         self.node = node
     }
 
-    public init?(markdown: String) {
+    public init(markdown: String) {
         guard let node = cmark_parse_document(markdown, markdown.utf8.count, 0) else {
-            return nil
+            fatalError("cmark_parse_document returned NULL. Should never happen.")
         }
         self.node = node
     }
@@ -63,25 +103,25 @@ public class Node: CustomStringConvertible {
         cmark_node_free(node)
     }
     
-    var type: cmark_node_type {
+    public var type: cmark_node_type {
         return cmark_node_get_type(node)
     }
     
-    var listType: cmark_list_type {
+    public var listType: cmark_list_type {
         get { return cmark_node_get_list_type(node) }
         set { cmark_node_set_list_type(node, newValue) }
     }
     
-    var listStart: Int {
+    public var listStart: Int {
         get { return Int(cmark_node_get_list_start(node)) }
         set { cmark_node_set_list_start(node, Int32(newValue)) }
     }
     
-    var typeString: String {
-        return String(cString: cmark_node_get_type_string(node)!)
+    public var typeString: String {
+        return String(unsafeCString: cmark_node_get_type_string(node)) ?? ""
     }
     
-    var literal: String? {
+    public var literal: String? {
         get { return String(unsafeCString: cmark_node_get_literal(node)) }
         set {
           if let value = newValue {
@@ -92,12 +132,19 @@ public class Node: CustomStringConvertible {
         }
     }
     
-    var headerLevel: Int {
+    public var start: Position {
+        return Position(line: cmark_node_get_start_line(node), column: cmark_node_get_start_column(node))
+    }
+    public var end: Position {
+        return Position(line: cmark_node_get_end_line(node), column: cmark_node_get_end_column(node))
+    }
+    
+    public var headerLevel: Int {
         get { return Int(cmark_node_get_heading_level(node)) }
         set { cmark_node_set_heading_level(node, Int32(newValue)) }
     }
     
-    var fenceInfo: String? {
+    public var fenceInfo: String? {
         get {
             return String(unsafeCString: cmark_node_get_fence_info(node)) }
         set {
@@ -109,7 +156,7 @@ public class Node: CustomStringConvertible {
         }
     }
     
-    var urlString: String? {
+    public var urlString: String? {
         get { return String(unsafeCString: cmark_node_get_url(node)) }
         set {
           if let value = newValue {
@@ -120,7 +167,7 @@ public class Node: CustomStringConvertible {
         }
     }
     
-    var title: String? {
+    public var title: String? {
         get { return String(unsafeCString: cmark_node_get_title(node)) }
         set {
           if let value = newValue {
@@ -131,7 +178,7 @@ public class Node: CustomStringConvertible {
         }
     }
     
-    var children: [Node] {
+    public var children: [Node] {
         var result: [Node] = []
         
         var child = cmark_node_first_child(node)
@@ -143,23 +190,25 @@ public class Node: CustomStringConvertible {
     }
 
     /// Renders the HTML representation
-    public var html: String {
-        return String(cString: cmark_render_html(node, 0))
+    ///
+    
+    public func html(options: RenderingOptions = RenderingOptions()) -> String {
+        return String(freeingCString: cmark_render_html(node, options.rawValue)) ?? ""
     }
     
     /// Renders the XML representation
-    public var xml: String {
-        return String(cString: cmark_render_xml(node, 0))
+    public func xml(options: RenderingOptions = RenderingOptions()) -> String {
+        return String(freeingCString: cmark_render_xml(node, options.rawValue)) ?? ""
     }
     
     /// Renders the CommonMark representation
-    public var commonMark: String {
-        return String(cString: cmark_render_commonmark(node, CMARK_OPT_DEFAULT, 80))
+    public func commonMark(options: RenderingOptions = RenderingOptions()) -> String {
+        return String(freeingCString: cmark_render_commonmark(node, options.rawValue, 80)) ?? ""
     }
     
     /// Renders the LaTeX representation
-    public var latex: String {
-        return String(cString: cmark_render_latex(node, CMARK_OPT_DEFAULT, 80))
+    public func latex(options: RenderingOptions = RenderingOptions()) -> String {
+        return String(freeingCString: cmark_render_latex(node, options.rawValue, 80)) ?? ""
     }
 
     public var description: String {
diff --git a/Sources/CommonMark/Reduce.swift b/Sources/CommonMark/Reduce.swift
new file mode 100644
index 0000000..3bfd8a5
--- /dev/null
+++ b/Sources/CommonMark/Reduce.swift
@@ -0,0 +1,112 @@
+//
+//  Reduce.swift
+//  CommonMark
+//
+//  Created by Chris Eidhof on 02.04.19.
+//
+
+import Foundation
+import Ccmark
+
+/// An algebra for a block-level element
+public struct InlineAlgebra<A> {
+    public var text: (_ text: String) -> A
+    public var softBreak: A
+    public var lineBreak: A
+    public var code: (_ text: String) -> A
+    public var html: (_ text: String) -> A
+    public var emphasis: (_ children: [A]) -> A
+    public var strong: (_ children: [A]) -> A
+    public var custom: (_ literal: String) -> A
+    public var link: (_ children: [A], _ title: String?,  _ url: String?) -> A
+    public var image: (_ children: [A], _ title: String?, _ url: String?) -> A
+}
+
+/// An algebra for a block-level element
+public struct BlockAlgebra<A> {
+    public var inline: InlineAlgebra<A>
+    public var list: (_ items: [A], _ type: ListType) -> A
+    public var listItem: (_ children: [A]) -> A
+    public var blockQuote: (_ items: [A]) -> A
+    public var codeBlock: (_ text: String, _ language: String?) -> A
+    public var html: (_ text: String) -> A
+    public var paragraph: (_ text: [A]) -> A
+    public var heading: (_ text: [A], _ level: Int) -> A
+    public var custom: (_ literal: String) -> A
+    public var thematicBreak: A
+    public var document: (_ children: [A]) -> A
+    public var defaultValue: A
+}
+
+extension Node {
+    public func reduce<R>(_ b: BlockAlgebra<R>) -> R {
+        func r(_ node: Node) -> R {
+            var children: [R] { return node.children.map(r) }
+            var lit: String { return node.literal ?? "" }
+            switch node.type {
+            case CMARK_NODE_DOCUMENT: return b.document(children)
+            case CMARK_NODE_BLOCK_QUOTE: return b.blockQuote(children)
+            case CMARK_NODE_LIST: return b.list(children, node.listType == CMARK_BULLET_LIST ? .unordered : .ordered)
+            case CMARK_NODE_ITEM: return b.listItem(children)
+            case CMARK_NODE_CODE_BLOCK: return b.codeBlock(lit, node.fenceInfo)
+            case CMARK_NODE_HTML_BLOCK: return b.html(lit)
+            case CMARK_NODE_CUSTOM_BLOCK: return b.custom(lit)
+            case CMARK_NODE_PARAGRAPH: return b.paragraph(children)
+            case CMARK_NODE_HEADING: return b.heading(children, node.headerLevel)
+            case CMARK_NODE_THEMATIC_BREAK: return b.thematicBreak
+            case CMARK_NODE_FIRST_BLOCK: return b.defaultValue
+            case CMARK_NODE_LAST_BLOCK: return b.defaultValue
+                
+                /* Inline */
+            case CMARK_NODE_TEXT: return b.inline.text(lit)
+            case CMARK_NODE_SOFTBREAK: return b.inline.softBreak
+            case CMARK_NODE_LINEBREAK: return b.inline.lineBreak
+            case CMARK_NODE_CODE: return b.inline.code(lit)
+            case CMARK_NODE_HTML_INLINE: return b.inline.html(lit)
+            case CMARK_NODE_CUSTOM_INLINE: return b.inline.custom(lit)
+            case CMARK_NODE_EMPH: return b.inline.emphasis(children)
+            case CMARK_NODE_STRONG: return b.inline.strong(children)
+            case CMARK_NODE_LINK: return b.inline.link(children, node.title, node.urlString)
+            case CMARK_NODE_IMAGE: return b.inline.image(children, node.title, node.urlString)
+            default:
+                return b.defaultValue
+            }
+        }
+        return r(self)
+    }
+}
+
+public protocol Monoid {
+    init()
+    static func +(lhs: Self, rhs: Self) -> Self
+    mutating func append(_ value: Self)
+}
+
+extension Monoid {
+    public mutating func append(_ value: Self) {
+        self = self + value
+    }
+}
+
+extension Array: Monoid { }
+
+extension Array where Element: Monoid {
+    public func flatten() -> Element {
+        return reduce(into: .init(), { $0.append($1) })
+    }
+}
+
+extension String: Monoid { }
+
+/// This collects all elements into a result `M`.
+///
+/// For example, to collect all links in a document:
+///
+///     var links: BlockAlgebra<[String]> = collect()
+///     links.inline.link = { _, _, url in url.map { [$0] } ?? [] }
+///     let allLinks = Node(markdown: string)!.reduce(links)
+public func collect<M: Monoid>() -> BlockAlgebra<M> {
+    let inline: InlineAlgebra<M> = InlineAlgebra<M>(text: { _ in .init() }, softBreak: .init(), lineBreak: .init(), code: { _ in .init()}, html: { _ in .init() }, emphasis: { $0.flatten() }, strong: { $0.flatten() }, custom: { _ in .init() }, link: { x,_,_ in x.flatten() }, image: { x,_, _ in x.flatten() })
+    
+    return BlockAlgebra<M>(inline: inline, list: { x, _ in x.flatten() }, listItem: { $0.flatten() }, blockQuote: { $0.flatten() }, codeBlock: { _,_ in .init() }, html: { _ in .init() }, paragraph: { $0.flatten() }, heading: { x,_ in x.flatten() }, custom: { _ in .init() }, thematicBreak: .init(), document: { $0.flatten() }, defaultValue: .init())
+}
diff --git a/Sources/CommonMark/SwiftAST.swift b/Sources/CommonMark/SwiftAST.swift
index f25174e..6de8480 100644
--- a/Sources/CommonMark/SwiftAST.swift
+++ b/Sources/CommonMark/SwiftAST.swift
@@ -11,8 +11,8 @@ import Ccmark
 
 /// The type of a list in Markdown, represented by `Block.List`.
 public enum ListType {
-    case Unordered
-    case Ordered
+    case unordered
+    case ordered
 }
 
 /// An inline element in a Markdown abstract syntax tree.
@@ -25,8 +25,8 @@ public enum Inline {
     case emphasis(children: [Inline])
     case strong(children: [Inline])
     case custom(literal: String)
-    case link(children: [Inline], title: String?, url: String?)
-    case image(children: [Inline], title: String?, url: String?)
+    case link(children: [Inline], title: String?, url: String)
+    case image(children: [Inline], title: String?, url: String)
 }
 
 extension Inline: ExpressibleByStringLiteral {
@@ -96,7 +96,7 @@ extension Block {
         case CMARK_NODE_BLOCK_QUOTE:
             self = .blockQuote(items: parseBlockChildren())
         case CMARK_NODE_LIST:
-            let type = node.listType == CMARK_BULLET_LIST ? ListType.Unordered : ListType.Ordered
+            let type = node.listType == CMARK_BULLET_LIST ? ListType.unordered : ListType.ordered
             self = .list(items: node.children.map { $0.listItem }, type: type)
         case CMARK_NODE_CODE_BLOCK:
             self = .codeBlock(text: node.literal!, language: node.fenceInfo)
@@ -158,12 +158,12 @@ extension Node {
     /// The abstract syntax tree representation of a Markdown document.
     /// - returns: an array of block-level elements.
     public var elements: [Block] {
-        return children.map(Block.init)
+        children.map(Block.init)
     }
 }
 
 func tableOfContents(document: String) -> [Block] {
-    let blocks = Node(markdown: document)?.children.map(Block.init) ?? []
+    let blocks = Node(markdown: document).children.map(Block.init)
     return blocks.filter {
         switch $0 {
         case .heading(_, let level) where level < 3: return true
@@ -211,7 +211,7 @@ extension Node {
         case let .list(items, type):
             let listItems = items.map { Node(type: CMARK_NODE_ITEM, blocks: $0) }
             self.init(type: CMARK_NODE_LIST, children: listItems)
-            listType = type == .Unordered ? CMARK_BULLET_LIST : CMARK_ORDERED_LIST
+            listType = type == .unordered ? CMARK_BULLET_LIST : CMARK_ORDERED_LIST
         case .blockQuote(let items):
             self.init(type: CMARK_NODE_BLOCK_QUOTE, blocks: items)
         case let .codeBlock(text, language):
diff --git a/Tests/CommonMarkTests/CommonMarkTests.swift b/Tests/CommonMarkTests/CommonMarkTests.swift
index 09795b5..a07b599 100644
--- a/Tests/CommonMarkTests/CommonMarkTests.swift
+++ b/Tests/CommonMarkTests/CommonMarkTests.swift
@@ -12,14 +12,14 @@ class CommonMarkTests: XCTestCase {
     
     func testMarkdownToHTML() {
         let markdown = "*Hello World*"
-        let html = markdownToHtml(string: markdown)
+        let html = markdowntoHTML(string: markdown)
         XCTAssertEqual(html, "<p><em>Hello World</em></p>\n")
     }
 
     func testMarkdownToNode() {
         let markdown = "*Hello World*"
         let rootNode = Node(markdown: markdown)
-        XCTAssertNotNil(rootNode)
+        XCTAssertEqual(rootNode.elements.count, 1)
     }
 
     func testMarkdownToArrayOfBlocks() {
@@ -33,8 +33,14 @@ class CommonMarkTests: XCTestCase {
             * List item 1
             * List item 2
             """
-        let rootNode = Node(markdown: markdown)!
+        let rootNode = Node(markdown: markdown)
         let blocks = rootNode.elements
         XCTAssertEqual(blocks.count, 4)
     }
+
+    func testReadMarkdownFromNonInvalidFilenameReturnsNil() {
+        let nonExistentFilename = "/lkjhgfdsa"
+        let rootNode = Node(filename: nonExistentFilename)
+        XCTAssertNil(rootNode)
+    }
 }
diff --git a/Tests/CommonMarkTests/XCTestManifests.swift b/Tests/CommonMarkTests/XCTestManifests.swift
new file mode 100644
index 0000000..b7cd9f5
--- /dev/null
+++ b/Tests/CommonMarkTests/XCTestManifests.swift
@@ -0,0 +1,21 @@
+#if !canImport(ObjectiveC)
+import XCTest
+
+extension CommonMarkTests {
+    // DO NOT MODIFY: This is autogenerated, use:
+    //   `swift test --generate-linuxmain`
+    // to regenerate.
+    static let __allTests__CommonMarkTests = [
+        ("testMarkdownToArrayOfBlocks", testMarkdownToArrayOfBlocks),
+        ("testMarkdownToHTML", testMarkdownToHTML),
+        ("testMarkdownToNode", testMarkdownToNode),
+        ("testReadMarkdownFromNonInvalidFilenameReturnsNil", testReadMarkdownFromNonInvalidFilenameReturnsNil),
+    ]
+}
+
+public func __allTests() -> [XCTestCaseEntry] {
+    return [
+        testCase(CommonMarkTests.__allTests__CommonMarkTests),
+    ]
+}
+#endif
diff --git a/Tests/LinuxMain.swift b/Tests/LinuxMain.swift
new file mode 100644
index 0000000..20912dc
--- /dev/null
+++ b/Tests/LinuxMain.swift
@@ -0,0 +1,8 @@
+import XCTest
+
+import CommonMarkTests
+
+var tests = [XCTestCaseEntry]()
+tests += CommonMarkTests.__allTests()
+
+XCTMain(tests)