- format_spec(+Format, -Spec:list) is semidet
- Parse a format string. Each element of Spec is one of the following:
- text(Text)
- Text sent to the output as is
- escape(Num, Colon, Action)
- A format escape. Num represents the optional numeric portion of
an esape. Colon represents the optional colon in an escape.
Action is an atom representing the action to be take by this
escape.