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.
This template can be substituted.
Usage
{{ifnotempty| x | A | B }}gives " A "{{ifnotempty|x| A | B }}gives " A "{{ifnotempty| | A | B }}gives " B "{{ifnotempty|| A | B }}gives " B "
Compare:
{{#if:x| A | B }}gives "A"{{#if:| A | B }}gives "B"
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 A and B. This produces either A or B, without trimming. The template's code is a substitution-safe version of
{{ {{#if: {{{1}}} | P1 | P2 }} |{{{2}}}|{{{3}}}}}