Regular Expressions 101

\ban ASCII word boundary

Group 1([a-z])?

?repeats the group contents below at most once:

Character Class[a-z]

a-zone character from a (97₁₀) to z (122₁₀) (case insensitive)

Group 2([a-z])?

?repeats the group contents below at most once:

Character Class[a-z]

a-zone character from a (97₁₀) to z (122₁₀) (case insensitive)

Group 3([a-z])?

?repeats the group contents below at most once:

Character Class[a-z]

a-zone character from a (97₁₀) to z (122₁₀) (case insensitive)

\2the text saved by group 2

\1the text saved by group 1

\ban ASCII word boundary

Global pattern flags

g modifier: global. Finds all matches instead of stopping after the first

i modifier: insensitive. Matches without distinguishing uppercase and lowercase letters

Detailed match information will be displayed here automatically.

Search reference

Regular Expression

\b([a-z])?([a-z])?([a-z])?\2\1\b

New

words   that   are   the   same backwards as forwards
e.g:
kayak, dewed, refer, hanah, but not hannah or henah or ana, nor wow or racecar.