<mtable>

[Lisahartun]

MathML Core treats <mtable> as a rigid table: if it is too wide, it simply overflows.
MathML 4 introduces rules allowing automatic line breaking of mathematical tables using the new breakstyle attribute.
For example:

<mtable breakstyle="after">
 '''
</mtable>
or
<mtable breakstyle="duplicate">
These values specify how operators should behave when a table is broken across lines.
For instance, a long system of equations
a + b + c + d + e = x
f + g + h + i + j = y
k + l + m + n + o = z
can now be broken automatically while preserving mathematical readability.
This functionality is not part of MathML Core. It is defined only in MathML 4.

Better support for equation arrays
MathML Core defines <mtable> purely as a table layout primitive.
MathML 4 explicitly discusses its use for: aligned equations, systems of equations, piecewise functions and matrices
and gives considerably more guidance and examples.
Example:
<mtable columnalign="right left">
  <mtr>
    <mtd><mi>x</mi></mtd>
    <mtd><mo>=</mo><mn>1</mn></mtd>
  </mtr>

  <mtr>
    <mtd><mi>y</mi></mtd>
    <mtd><mo>=</mo><mn>2</mn></mtd>
  </mtr>
</mtable>

New line-breaking model for matrices
Consider a large matrix
⎡ a  b  c  d  e  f ⎤
⎢ g  h  i  j  k  l ⎥
⎣ m  n  o  p  q  r ⎦

MathML 4 introduces line-breaking support that allows large mathematical tables to participate in automatic layout instead of simply overflowing.

Additional control of repeated operators
Suppose an aligned derivation contains repeated equals signs:
A = B
  = C
  = D
MathML 4 introduces the concept of how operators should behave when an equation array is broken across lines (for example, whether an operator should be duplicated or moved to the next line).
These behaviours are controlled through values such as breakstyle="before", breakstyle="after", breakstyle="duplicate"

Better integration with MathML Full
MathML Core intentionally treats <mtable> as a rendering primitive.
MathML 4 integrates <mtable> with the broader MathML Full model, particularly: line breaking, elementary mathematics, compatibility with legacy MathML table features.
<mtable> becomes part of a richer layout model rather than remaining only a static table element.