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# Regular Expressions - Operator Precedence Regular expressions are evaluated from left to right and follow an order of precedence, which is very similar to arithmetic expressions. Operations with the same precedence are evaluated from left to right, while operations with different precedence are evaluated from higher to lower. The following table explains the precedence order of various regular expression operators from highest to lowest: | Operator | Description | | --- | --- | | | Escape character | | (), (?:), (?=), [] | Parentheses and square brackets | | *, +, ?, {n}, {n,}, {n,m} | Quantifiers | | ^, $, any metacharacter, any character | Anchors and sequences (i.e., position and order) | | | | Alternation, "OR" operation. Characters have higher precedence than the alternation operator, so "m|food" matches "m" or "food". To match "mood" or "food", use parentheses to create a subexpression, resulting in "(m|f)ood". | Here are some common regular expression operators in order of precedence from highest to lowest: * **Escape Symbol:** `` is the escape symbol used to escape other special characters. It has the highest precedence. Example: `d`, `.`, etc., where `d` matches a digit, `.` matches a dot. * **Parentheses:** Parentheses `()` are used to create subexpressions and have higher precedence than other operators. Example: `(abc)+` matches "abc" one or more times. * **Quantifiers:** Quantifiers specify the number of times the preceding element can repeat. Example: `a*` matches zero or more "a"s. * **Character Classes:** Character classes are denoted by square brackets `[]` and are used to match any character within the brackets. Example: `` matches any vowel. * **Assertions:** Assertions are elements used to check conditions at specific positions in a string. Example: `^` represents the start of a line, `$` represents the end of a line. * **Concatenation:** Concatenation represents the simple joining of characters in the absence of other operators. Example: `abc` matches "abc". * **Pipe:** The pipe symbol `|` represents an "OR" relationship, used to choose one among multiple patterns. Example: `cat|dog` matches "cat" or "dog". Next, let's look at the precedence explanation for the following regular expression: d{2,3}|+(abc)* * `d{2,3}` matches two to three digits. * `|` represents OR. * `+` matches one or more lowercase letters. * `(abc)*` matches zero or more "abc"s.