@timriley I still use ERb.
I used to be really into HAML until I started getting into AngularJS where you make heavy use of custom attributes (e.g. ng-foo="bar") and HAML didn't make that nice to use. I don't do AngularJS these days, but I never got back into alternative templating engines either.
It looks like Slim has great support for custom attributes out of the box.
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