Grep for the win
Limitation of SuperMemo search feature
SuperMemo search is limited to plain text and there is no support for regular expressions as searches are implemented using assembly language. This is not the end. You can overcome such limitation by using a third party tool and searching into the files externally. My prefered choice is grepWin, a free and open source solution.
GrepWin
grepWin is a simple search and replace tool which can use regular expressions to do its job. This allows to do much more powerful searches and replaces.
Download: GitHub
HTML search
HTML collection search
Cross collection HTML search
Perhaps the biggest perk of using grep is that you can access to all .htm files in your SuperMemo, not limited to a particular collection. This is specially useful if you use multiple collections in the same language.