14.4 \settodepth

Synopsis:

\settodepth{\len}{text}

Set the length \len to the depth of box that LaTeX gets on typesetting the text argument. The length name \len has to be a control sequence (see Control sequence, control word and control symbol), and as such must begin with a backslash, \ under normal circumstances.

This will print how low the character descenders go.

\newlength{\alphabetdepth}
\settodepth{\alphabetdepth}{abcdefghijklmnopqrstuvwxyz}
\the\alphabetdepth

If you did not declare \len with \newlength, if for example you mistype the above as \settodepth{\aplhabetdepth}{abc...}, then you get something like ‘Undefined control sequence. <argument> \aplhabetdepth’. If you leave the backslash out of \len, as in \settodepth{alphabetdepth}{...} then you get something like ‘Missing number, treated as zero. <to be read again> \setbox’.