The BELOW element

Permitted Context: %math
Content Model: %math

The <BELOW> element is used to draw a line, arrow, or curly bracket below the expression enclosed by this element. For example:

    <below>X + Y</below>    giving   X + Y
                                     _____

    <below sym=rarr>X + Y</below>   giving   X + Y
                                             ---->

You can also place an expression centered below the line or arrow with the SUP element or its shortref form, for example:

<above sym=cub>n(n - 1)(n - 2)&dots;(n - m + 1)</above>
<sup><text>total of m factors</text></sup>

which would be rendered as (within limits of ascii art):

    n(n - 1)(n - 2) ... (n - m + 1)
    \---------------v-------------/
           total of m factors

I can't find the ISO entity names for under/over curly brackets!

Permitted Attributes

SYM
An entity name for a stretchy symbol, e.g. cub for a curly bracket (brace). Defaults to line. The other choices are: larr (left arrow), rarr (right arrow), hat and tilde.

Note: Don't include the & prefix, so <below sym="→"> is wrong!