Tasmota/lib/libesp32/re1.5

What is re1.5?
==============

re1 (http://code.google.com/p/re1/) is "toy regular expression implementation"
by Russel Cox, featuring simplicity and minimal code size unheard of in other
implementations. re2 (http://code.google.com/p/re2/) is "an efficient,
principled regular expression library" by the same author. It is robust,
full-featured, and ... bloated, comparing to re1.

re1.5 is an attempt to start with re1 codebase and add features required for
minimalistic real-world use, while sticking to the minimal code size and
memory use.

Why?
====
re1.5 is intended for use in highly constrained, e.g. embedded, environments,
where offering familiar high-level string matching functionality is still
beneficial.

Features
========

* Like re1, re1.5 retains design where compiled expression can be executed
(matched) by multiple backends, each with its own distinctive design and
runtime properties (complexity and memory usage).
* Unlike re1, regexes are compiled to memory-efficient bytecode. Exact size
of the bytecode can be found prior to compilation (for memory allocation).
* External API functions feature namespace prefix to improve clarity and
avoid name clashes when integrating into other projects.
* Matchers are NUL-char clean and take size of the input string as a param.
* Support for quoted chars in regex.
* Support for ^, $ assertions in regex.
* Support for "match" vs "search" operations, as common in other regex APIs.
* Support for named character classes: \d \D \s \S \w \W.

TODO
====

* Support for repetition operator {n} and {n,m}.
* Support for Unicode (UTF-8).
* Support for matching flags like case-insensitive, dot matches all,
multiline, etc.
* Support for more assertions like \A, \Z.

Author and License
==================
re1.5 is maintained by Paul Sokolovsky pfalcon at users.sourceforge.net and
licensed under BSD license, just as the original re1.