\placetable[here]{none}
\starttable[|l|l|]
\HL
\NC first
\NC second
\NC\AR
\HL
\NC a\letterunderscore{}b
\NC 1.6
\NC\AR
\NC \$a\letterunderscore{}b\$
\NC 2.5
\NC\AR
\HL
\stoptable