Rows

(Excerpt from "The MathML Handbook" by Pavi Sandhu)

The mrow element is used to group together any number of related subexpressions. The arguments of the mrow element are visually rendered in a horizontal row from left to right, in the order they occur. This element is important because:

  • It provides guidance for proper spacing between its arguments.
  • It provides information about linebreaking and indentation.
  • It provides information on the meaning of the markup that is useful for audio renderers or computer algebra systems.
  • It specifies the grouping of subexpressions into arguments.
  • It specifies the scope of stretchable operators.

In general, multiple mrow elements are nested inside each other to reflect the tree structure of the expression being represented. Typically, each mrow element has as its arguments a single operator along with the operands that are being acted upon, as shown here:

x + 2y - 1x

<mrow>
  <mi>x</mi>
  <mo>+</mo>
  <mrow>
    <mn>2</mn>
    <mo>&InvisibleTimes;</mo>
    <mi>y</mi>
  </mrow>
  <mo>-</mo>
  <mn>1</mn>
</mrow>

The presence of an mrow element is automatically inferred around the content of certain presentation elements, if they occur with a number of arguments different from 1, as explained under Presentation markup: Introduction.

It is possible to add additional mrow elements to an expression without changing its meaning. This is not a MathML error and does not affect the validity of the expression. However, to avoid any additional overhead in processing the markup it is a good practice in general to use the smallest number of mrow elements that are necessary. This is because each extra mrow element adds another level in the document tree and requires you to create an extra bounding box; for example, when you apply a CSS stylesheet to the expression.

   

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