[Tex/LaTex] “! You can’t use `\raise’ in internal vertical mode” error

Question

I used the command \raise to superimpose a title to a writing.

I got the error

! You can't use `\raise' in internal vertical mode

which puzzled me for a while.

For those interested, here is my code :

\def\withHatTitle#1#2{% #1: title #2: content
\setbox1=\hbox{#2}
\setbox0=\hbox{%\leaders\hrule height3pt depth-2pt\hskip 5pt
\kern\fboxsep#1\kern\fboxsep\leaders\hrule height3pt depth-2pt\hskip 5pt}
\ifdim\wd1<\wd0\wd1=\wd0\fi% if title longer than content, title gives the size
\setbox0=\hbox{\makebox[\wd1]{\box0\leaders\hrule height3pt depth-2pt\hfill}}% complete title with hrule
\wd1=0pt \box1 \raise 11pt \box0}% superpose title and content

Answer 1

The explanation for this error is that \raise is forbidden in vertical mode, that is roughly when Tex piles up boxes in vertical.

Thus, the solution is simple : exit from the vertical mode. A simple solution consists in enclosing my macro \withHatTitle with a \hbox command, as follows:

\hbox{\withHatTitle{The title}{This is the text to be titled}}

Hope this helps !

P.S. the former is true also with \lower.