Every character that cannot be a macro identifier can be escaped with a backslash \. If you try to escape a macro identifier it of course treats the thing as a macro instead and fails, e.g. in \a it would try to use a macro called \a, not escape the character a.
For some characters, escaping or not does not make any difference because they don't have any meaning to OurBigBook Markup, e.g. currently % is always the exact same as \%.
But in non-literal macro arguments, you have to use a backslash to escape the following if you want them to not have any magical meaning:
Furthermore, only at:
  • at the start of the document
  • after a newline
  • at the start of a new argument
you must also escape the following macros with insane shortcut:
The escape rules for literal arguments are described at: Section "Literal arguments ([[...]] and {{key=...}})".
This is good for short arguments of regular text, but for longer blocks like code blocks or mathematics, you may want to use literal arguments