GPU implementations of PCRE compatible regex engines that are faster compared to CPU implementations. The bracket syntax happens to be covered by regex in such an example. Many modern regex engines offer at least some support for [[Unicode]]. A regex "pattern" matches a target "string". RE/flex offers a choice of regular expression pattern matchers&colon; RE/flex regex and Boost. The character class is the most basic regex concept after a literal match. Additionally, the functionality of regex implementations can vary between [[Software versioning|version]]s. If a regex is named, the modifier comes after the name. The regular-expression engine is derived from regex written by Henry Spencer. Many programming languages provide regex capabilities either built-in or via libraries. Therefore, this regex matches, for example, 'a ', or 'ax', or 'a0'. For example, consider an add-on library for regex support on codice 23. Patterns range from extremely simplistic to deeply complex (analogous to Regex but aimed for NL). In "Apocalypse 5", Larry Wall enumerated 20 problems with "current regex culture". Some languages and tools such as [[Boost C++ Libraries|Boost]] and [[PHP]] support multiple regex flavors.