Force whitespace (html entity?) at end of string (beat trim)

Question

How can I trick a trimming function not to remove whitespace at the end of a string?

  would normally do fine but my strings are long, so I do want them to break.

Is there no html entity for whitespace?

This is not a specific coding language question (it's complicated).

It's for MediaWiki and I want to replace underscores with normal whitespace: {{#replace:Foo_Bar.png|_| }}

Edit: Solution:  

Answer 1

{{#replace:Foo_Bar.png|_|<nowiki> </nowiki>}}     (documentation)