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In these ranges, " " (space) is the character immediately following the control characters, "!" is the character immediately following space, and "" is U+10FFFF, the last character in Unicode. Thus, the range from " " to "" includes all characters except for control characters (of which articles may contain newlines and tabulation ...
Given regular expressions R and S, the following operations over them are defined to produce regular expressions: (concatenation) (RS) denotes the set of strings that can be obtained by concatenating a string accepted by R and a string accepted by S (in that order). For example, let R denote {"ab", "c"} and S denote {"d", "ef"}.
Regular Expression Flavor Comparison – Detailed comparison of the most popular regular expression flavors; Regexp Syntax Summary; Online Regular Expression Testing – with support for Java, JavaScript, .Net, PHP, Python and Ruby; Implementing Regular Expressions – series of articles by Russ Cox, author of RE2; Regular Expression Engines
This is the "regular expression" (or regexp, or regex). Its metacharacters can represent multiple possibilities for a character position or a range of character positions within a page, using metacharacters for truth logic, grouping, counting, and modifying the characters to be found.
Say the search box is given two words.The search starts with two index lookups, and the two results are combined with a logical AND. But before they are displayed as search results, they must all be assigned a final score before the top twenty (listed on the first page) can be displayed, and they must be formatted with snippets and highlighting.
In SQL, wildcard characters can be used in LIKE expressions; the percent sign % matches zero or more characters, and underscore _ a single character. Transact-SQL also supports square brackets ([and ]) to list sets and ranges of characters to match, a leading caret ^ negates the set and matches only a character not within the list.
All these involve insource:/slash delimited regex/ with filters. Any search link with an insource:/regex/ search should always provide the additional query terms that would filter (reduce) the search domain as much as possible. This template defaults to article space if no namespace is given, which is a filter.
The wildcard pattern (often written as _) is also simple: like a variable name, it matches any value, but does not bind the value to any name. Algorithms for matching wildcards in simple string-matching situations have been developed in a number of recursive and non-recursive varieties.