From HacDC Wiki
This is an auxiliary template allowing to encode "
within template parameters. It is unnecessary to get a
|" in these cases, better use "
for this purpose. However the "
|" delimiter for a
Wiki table has to be escaped by a template if it's used
within a template, see also w:WP:QIF.
Note that there's no such problem with "
!" (exclamation mark), it
only affects "
|" (vertical bar) in conjunction
with the m:Help:Parameter default mechanism within tables.