Documentation
With this template #if can be used in a way such that it does not strip spaces and newlines from the "then" and "else" part. For evaluating the condition spaces and newlines are stripped like with ParserFunctions.
Usage
{{ifnotempty|x| p | q }}gives " p "{{ifnotempty|| p | q }}gives " q "
Compare:
{{#if:x| p | q }}gives "p"
Internal technical details
For evaluating the condition (determining non-emptiness of the first parameter) the template uses parser function #if, producing 1 if the condition is true, and 2 otherwise. The template with name equal to "P" followed by the index value produced (hence Template:P1 or Template:P2), is called with as parameters p and q. This produces either p or q, without trimming.