Regular Expressions 101

Positive Lookbehind(?<=[\s>]|^)

1st Alternative[\s>]

Character Class[\s>]

\sany whitespace character

>the literal > (62₁₀ / 76₈ / 3E₁₆)

2nd Alternative^

^start of string

#the literal # (35₁₀ / 43₈ / 23₁₆)

Group 1(\w*[A-Za-z_]+\w*)

\w*any word character, repeated any number of times

Character Class[A-Za-z_]+

+matches at least one character from the set below:

A-Zone character from A (65₁₀) to Z (90₁₀) (case sensitive)

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

_the literal _ (95₁₀ / 137₈ / 5F₁₆)

\w*any word character, repeated any number of times

\ban ASCII word boundary

Negative Lookahead(?!;)

;the literal ; (59₁₀ / 73₈ / 3B₁₆)

Global pattern flags

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

Detailed match information will be displayed here automatically.

Search reference

Regular Expression

(?<=[\s>]|^)#(\w*[A-Za-z_]+\w*)\b(?!;)

New

Here's a #hashtag and here is #not_a_tag; which should be different. Also testing: Mid#hash. #123 #!@£ and <p>#hash</p>