Space in \printuntil regex needs to be protected

[\printline and friends support regex|
https://doc.qt.io/qt-6/07-0-qdoc-commands-includingexternalcode.html#printline]:

If the substring argument is surrounded by slashes it is interpreted as a regular expression.

Example that is used is for detecting a closing bracket 'at the right level':

   \printuntil /^\}/

Anyhow, when the closing bracket is prefixed with some spaces, one need to specially protect the spaces. This works:

   \printuntil /^\ \ \ \ \}/

while this doesn't :

   \printuntil /^    \}/

This is surprising, as whitespace normally doesn't need to be protected. This should either be fixed or documented.