Function rt_format::parser::parse_specifier

pub fn parse_specifier<V, S>(
    spec_str: &str, 
    value_src: &mut S
) -> Result<Specifier, ()> where
    V: FormatArgument,
    S: ArgumentSource<V>, 

Parses only the format specifier portion of a format argument. For example, in a format argument specification {foo:#X}, this function would parse only the #X part.