230 {<<#408#>math commands<#408#>>}
In LaTeX~2.09, if you wanted a command to work both in math mode and
in text mode, the suggested method was to define something like:
verbatim20
Unfortunately, the 231 stops 232 changing size correctly in (for
instance) subscripts or a fraction.
In LaTeX2e<#410#><#410#> you can define it thus:
verbatim21
Now 233 will work correctly in all contexts.
This is because the 234 does nothing, producing simply
235, when 236 is used within math mode; but it ensures that math
mode is entered (and exited) as required when 237 is used in text
mode.