The definition of SetCategory above is missing an important component: its library documentation. documentation Here is its definition, complete with documentation.
Documentary comments are an important part of constructor definitions. Documentation is given both for the category itself and for each export. A description for the category precedes the code. Each line of the description begins in column one with ++. The description starts with the word Description:.Other information such as the author's name, date of creation, and so on, can go in this area as well but are currently ignored by Axiom. All lines of the description following the initial line are indented by the same amount.
Surround the name of any constructor (with or without parameters) with an {\bf }. Similarly, surround an operator name with {\tt }, an Axiom operation with {\bf }, and a variable or Axiom expression with $$. Library documentation is given in a TeX-like language so that it can be used both for hard-copy and for Browse. These different wrappings cause operations and types to have mouse-active buttons in Browse. For hard-copy output, wrapped expressions appear in a different font. The above documentation appears in hard-copy as:
SetCategory is the basic category for describing a collection of elements with = (equality) and a coerce to OutputForm.
and
tests if and are equal.
For our purposes in this chapter, we omit the documentation from further category descriptions.