Here is the general form of a format code, where optional
parts in [brackets], and actual characters are
in "double quotes":
"{" [name] ["!" conversion] [":" spec] "}"
For the
portion, see Section 9.4.2, “The namename part”.
For the part, see Section 9.4.3, “The conversionconversion
part”.
For the spec part, see Section 9.4.4, “The spec part”.