Re /language-reference-guide/system-functions/system-functions-by-category/

This page would benefit from being reworked.

• The sections should be presented in a sensible order.
• Each section should have introductory text about the purpose of the functions in that category.
• The functions in each category should be validated and amended as necessary.

At a later date it might be valid to differentiate system constants, variables, etc from other system variables, but for now they should remain part of this page.