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600 lines of code, 9 contributors for 20 line code problem
It’s therefore difficult to understand completely.
A lot bugs arise from people using Mustache and using {{ }} instead of {{{ }}}. The later format is required if you have data which includes & < and > characters. Not using the later form results in subtle bugs that only show up later.
It’s not bad compared to some templating frameworks but having conditional if/not support is starting down the path of building a bad language.
It has unnecessary features like template caching - which exchanges speed for memory usage and adds complexity - premature optimization and a simpler library will be faster. This optimizing for a complicated design.