[texhax] unexplained space

Thu May 17 10:59:03 CEST 2007

On Tuesday 08 May 2007 2:23 pm, Toby Cubitt wrote:
> Philip G. Ratcliffe wrote:
>
> Out of curiosity, I've always wondered whether there are any
> circumstances where this would hurt (beyond the obvious one when a
> newline is breaking two separate words)?

Yesterday I was hit by the following (then my head hit the desk, hard):

\somemacro%
{blahblah}%
{http://somewhere}

\somemacro being:

\def\somemacro#1{\domesomething#1\begingroup\Url}

i.e. \somemacro gobbled {blahblah} as it should, and by intention let the
processing of {http://somewhere} to the url package.  Poor \Url did his
usual tricks with catcodes and looked for a delimiter---and found what?
A percent character.  Satisfied, it searched for the next percent, screwing
the layout in interesting ways.

It may be worth noting that plain \url in place of \begingroup\Url would
not find the url, even when I removed the percent characters; it is only
\Url which skipped the following whitespace.

bit,