Thanks to 
CodePudding user response：
So after many attempts at using case, I decided to try an alternative method - and it worked! It isn't too much longer, but here it is.
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{%- elsif icon contains 'patternsbooks' -%}
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{%- endif -%}
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</div>
It seems to be the only way I have managed to make it work.
I am still curious as to whether using case is still possible, so if anyone has more information, it would be greatly appreciated!
EDIT: Streamlined the code as to not replicate the svg element multiple times.
CodePudding user response：
Your problem is solved by a simple technique of debugging. Use the common HTML comment to establish your test condition or case makes sense. I am pretty sure you will surprise yourself here. Here is that secret sauce:
<!-- Secret here >>> {{icon | strip | strip_newlines}} -->
You can run your code, and then search the generated source for Secret. When you see what the Liquid parse generated, you will have proof of the test conditions to use to test with in your case statements. That case/when test is exact whereas your if statement approach is loose, using contains.
Once you know why your test condition works loosely, maybe you'll see the pattern where you could flip back to using the more precise case.