Message
mml @columnalign attribute must contain values from the list 'left', 'center', 'right'
Rule XPath:
This rule ASSERTS the following, raising an alert if FALSE:
every $value in tokenize(@columnalign) satisfies $value = ('left', 'center', 'right')
Additional Information
The mml @columnalign attribute specifies horizontal alignment of a cell with respect
to other cells of the same column.
On elements mml:math, mml:tr, mml:mlabeledtr, mml:mstyle, mml:mtable this attribute
can hold one or more space-separated values.
On element mml:mtd this attribute can hold one value (this is enforecd by the DTD).