Regular Expression (regex - regexp)

Regular Expression (regex - regexp) is a sequence of characters that define a search pattern. Usually such patterns are used by string searching algorithms for “find” or “find and replace” operations on strings, or for input validation

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Symbolic Expression (s-expression - sexprs - sexps)

Symbolic Expression (s-expression - sexprs - sexps) are a notation for nested list (tree-structured) data, invented for and popularized by the programming language Lisp. also used in text-format WebAssembly

s-expressions are used to represent both:

• source code
• data

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Meta Expression (m-expression)

Meta Expression (m-expression) was an early proposed syntax for the Lisp programming language

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Indentation Expression (i-expression)

Indentation Expression (i-expression) uses indentation to indicate parentheses implicitly, and are thus in some ways intermediate between S-expressions and M-expressions. I-expressions were introduced in Scheme Request For Implementation 49 as an auxiliary syntax for Scheme, but they have not been widely adopted

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