A formula is written as plain text and translated to MathML. Text left
bare inside a row is not drawn by the browser, so a token without an
element disappears: every multi-digit number did. `a = floor((14 - month)
/ 12)` came out as `a = floor ( ( - month ) )`, and `year + 4800` as
`year + `. The markup looked reasonable at a glance, and the numbers were
simply gone.
The classification now covers every kind of text and has no bare output.
A number of any length is `mn`; one letter of any script is an identifier,
so Greek stays a variable rather than becoming upright text; an operator,
including one written with its spacing, is `mo`; a space is an explicit
`mspace`; and anything else is `mtext` rather than nothing.
A test walks every document in both languages and compares the characters
the page would show against the characters the formula was written with.
It found three more formulas dropping a sign, and it now guards the whole
set: ninety-six formula blocks, checked on every run rather than by
looking at a page. Only letters and digits are compared, because the
other characters in a formula source are notation — `^`, `_`, `*`,
`/`, braces, and the word `sqrt`, which is drawn as a radical sign.
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