# 0.7 Presentation layout elements (mrow, mfrac, msqrt, mroot)

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Lay out elements are responsible for two dimensional structure, arrangement and final appearnce by the rendering system.

Layout elements control two dimensional layout of characters, symbols and composed expressions. There are three groups of elements that determine the two dimensional lay out of the mathematical content and affects its maangement.

## Layout element groups

• Basic layout elements
• Scripting elements
• Table elements

Basic layout elements comprises of 10 elements. The names and their basic role in rendering layout are listed here :

## Basic layout elements

• “mrow” : makes horizontal groups of sub-expressions for variety of purposes
• “mfrac : renders elements in P/Q form
• “msqrt” : renders a square root
• “mroot” : renders a radical with an index
• “mstyle : set environment attributes for the enclosed elements
• “merror : enclose a syntax error message from a preprocessor
• “mpadded” : manages space around content
• “mphantom” : makes content invisible, while maintaining structure
• “mfenced” : Segregates terms with separators and surround its content with a pair of fences
• “menclose” : enclose content with a stretching symbol

## ”mrow” layout element

The “mrow” element is a horizontal sub-grouping facility. Grouping of sub expression is an important requirement for variety of reasons. Primarily, this element determines the relationship between an “operator” and “operand”. When there is single character “operator” and “operand” relationship, then grouping is not an issue. However, when there more than one “operand” in an expression, then grouping is required.

Grouping of elements is also important where elements require certain numbers of argument. In such situation, it is possible that there are more child elements than the arguments required. Consider the example here, where child elements are grouped to meet the requirement of “mfrac” syntax for two arguments.

## "mfrac" layout element

<m:math display="block"> <m:mfrac> <m:mrow> <m:mi>x</m:mi> <m:mo>+</m:mo> <m:mn>y</m:mn> </m:mrow> <m:mn>z</m:mn> </m:mfrac> </m:math>

Save the file after editing as “test.xml”. The display looks like :

$\frac{x+y}{z}$

In the example above, “mrow” element is used to group the sub-expression “x + y” to be treated as numerator in “mfrac” implementation.

We have also seen earlier that “mrow” plays important role in determining the form of an operator. The form of an operator as “prefix” or “infix” or “postfix” is determined by the position of an operator in the group of sub expression defined by “mrow” element.

Grouping of elements, terms and sub-expressions (in yet another sub-expression) is a common requirement for meaningful mathematical expression. As such, MathML platform implements an inferred mechanism, whereby certain elements infer that the child elements are grouped with “mrow” in an implicit manner. This means that we may save on writing a pair of “mrow” tags in such situation.

#### Questions & Answers

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