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:Help:Conditional tables. 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.