1. Open the Find dialog, tick the "Regular Expressions" checkbox, close the dialog.
2. Select any text that contains characters that play special role in regular expressions (for example, perl variables look like $something), press Ctrl+F3.
3. The selected text will be treated as a regular expression, not as text itself, and therefore even the selected text will not be found.

I think, in such situation EmEditor should just internally escape all the meta-characters that happened to be present in the selected block.