Before you pan mini-languages, take a look at the Parrot distribution. Parrot uses preprocessing and mini-languages extensively to make it easier to maintain. Opcodes, the JIT compiler, and PMC (variable) classes are largely written in mini-languages. Documentation is in a mini-language you may have heard of called POD. Configure uses a simple templating mini-language extensively--often to generate Makefiles, another mini-language. Code for Parrot is written in Parrot assembly, but a huge portion of the core is devoted to handling Parrot Intermediate Representation, a mini-language that makes the assembler more usable by offering friendlier syntax and automatically allocating registers.
Used judiciously, mini-languages can save a great deal of time. HTML templating isn't necessarily the right time, but that doesn't mean they're not useful in other situations.
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