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# 1.4. A note on regular expressions

Orange Textable widgets rely heavily on regular expressions (or regexes), which are essentially a body of conventions for describing a set of strings by means of a single string. These conventions are widely documented in books and on the Internet, so we will not give here yet another introduction to this topic. Nevertheless, a basic knowledge of regexes is required to perform any non-trivial task with Orange Textable, and more advanced knowledge to fully exploit the software’s possibilities.

The syntax of regexes is partly standardized, but some variations remain. Orange Textable uses Python regexes, for which Python documentation is the best source of information. In particular, it features a good introduction to regexes. A first reading might be limited to the following sections:

> - Simple Patterns
> - More Metacharaters

Also recommended are the following:

> - Compilation Flags
> - Lookahead Assertions
> - Greedy vs. Non-Greedy

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