# Empty

//

# Basic sequence

/abc/

# Repetition

/a*b+c?d/

/a{4,8}/

/a{,8}/

/a{3,}/

/a{7}/

# Alternation

/foo|bar/

# Character classes

/[abc]/

/[a-fA-F0-9_]/

/\A[+-]?\d+/

/[\w]+/

/\[\][123]/

/[^A-Z]/

/[]]/ # MRI gives a warning, but accepts this as matching ']'

/[^]]/ # MRI gives a warning, but accepts this as matching anything except ']'

/[^-]/

/[|]/

# Nested character classes

/[[a-f]A-F]/ # BAD - not parsed correctly

# Meta-character classes

/.*/

/.*/m

/\w+\W/

/\s\S/

/\d\D/

/\h\H/

/\n\r\t/

# Anchors

/\Gabc/

/\b!a\B/

# Groups

/(foo)*bar/

/fo(o|b)ar/

/(a|b|cd)e/

/(?::+)\w/ # Non-capturing group matching colons

# Named groups

/(?<id>\w+)/

/(?'foo'fo+)/

# Backreferences

/(a+)b+\1/

/(?<qux>q+)\s+\k<qux>+/

# Named character properties using the p-style syntax

/\p{Word}*/

/\P{Digit}+/

/\p{^Alnum}{2,3}/

/[a-f\p{Digit}]+/ # Also valid inside character classes

# Two separate character classes, each containing a single POSIX bracket expression

/[[:alpha:]][[:digit:]]/

# A single character class containing two POSIX bracket expressions

/[[:alpha:][:digit:]]/

# A single character class containing two ranges and one POSIX bracket expression

/[A-F[:digit:]a-f]/

# *Not* a POSIX bracket expression; just a regular character class.

/[:digit:]/

# Simple constant interpolation

A = "a"

/#{A}bc/

# unicode

/\u{9879}/