|re2c| works as a preprocessor. It reads the input file (which is usually a
program in |lang_name|, but can be anything) and looks for blocks of code
enclosed in special-form start/end markers. The text outside of these blocks is
copied verbatim into the output file. The contents of the blocks are processed
by |re2c|. It translates them to code in |lang_name| and outputs the generated
code in place of the block.
