Description:

The package provides commands for "splitting" a token list at
the first occurrence of another (specified) token list. I.e.,
for given token lists s, t return b and the shortest a, such
that t = a s b. The package's mechanism differs from those of
packages providing similar features, in the following ways: -
the method uses TeX's mechanism of reading delimited macro
parameters; - the splitting macros work by pure expansion,
without assignments; - the operation is carried out in a single
macro call. A variant of the operation is provided, that
retains outer braces.