libxstr-ocaml-dev 0.2.1-21build6 (arm64 binary) in ubuntu wily

 xstr is an OCaml library for string operations.
 .
 This package implements frequent string operations: searching,
 replacing, splitting, matching. It is independent from the Str library,
 and can replace Str in many cases. Unlike Str, xstr is thread-safe.
 xstr does not implement regular expressions in general, but an
 important subset. Some operations of xstr are performed as quickly as
 by Str; if the string to be processed is small, xstr is often faster
 than Str; if the string is big, xstr is up to half as fast than Str.