Provides a set of functions to facilitate building formatted strings under
various replacement rules: C-style formatting, variable-based formatting,
and number-based formatting. C-style formatting is basically identical to
built-in function 'sprintf'. Variable-based formatting allows users to put
variable names in a formatted string which will be replaced by variable
values. Number-based formatting allows users to use index numbers to
represent the corresponding argument value to appear in the string.
