The test file for TeX and LaTeX includes additional toy examples.
Examples of possible modifications, to source files from the public domain, are also offered. The proposed modifications are minimal, but some of them got quite complex due to a self-imposed restriction that they should be placed in the preambles, without altering the source code. Such restrictions are typically insignifant for well-written source files of LaTeX, while are more difficult to satisfy within TeX files that tend to employ low-level commands.