regex101: Find CSS Class with ability to replace

Explanation

Pro

Group 1(class=(\\?(?:"|'){1,2})(?:[-a-z0-9 ]* )?)

class=the literal text class= (case insensitive)

Group 2(\\?(?:"|'){1,2})

\\?optionally matches the literal \ (92₁₀ / 134₈ / 5C₁₆)

Non-Capturing Group(?:"|'){1,2}

{1,2}repeats the group contents below between 1 and 2 times:

1st Alternative"

"the literal " (34₁₀ / 42₈ / 22₁₆)

2nd Alternative'

'the literal ' (39₁₀ / 47₈ / 27₁₆)

Non-Capturing Group(?:[-a-z0-9 ]* )?

?repeats the group contents below at most once:

Character Class[-a-z0-9 ]*

*matches any number of characters from the set below:

-the literal - (45₁₀ / 55₈ / 2D₁₆)

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

0-9one character from 0 (48₁₀) to 9 (57₁₀)

the literal (32₁₀ / 40₈ / 20₁₆)

successthe literal text success (case insensitive)

Positive Lookahead(?=\2|\s)

1st Alternative\2

\2the text saved by group 2

2nd Alternative\s

\sany whitespace character

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

Quick Reference

26 tokens

Regular Expression

(class=(\\?(?:"|'){1,2})(?:[-a-z0-9 ]* )?)success(?=\2|\s)

New

// Match these
class='something success'
class="success"
class='something success another"
class="something-else success test"
class=\'success\'
class=\"success\"
class=\"modal success text-success\"
class='    success'
CssClass="old-asp-way success"
response.WriteLine("	<div class=""success""></div>")
response.WriteLine('	<div class=''whatever success something''></div>')

// Don't match these
class="text-success"
class="success-something"

Substitution

$1changed

// Match these
class='something success'
class="success"
class='something success another"
class="something-else success test"
class=\'success\'
class=\"success\"
class=\"modal success text-success\"
class='    success'
CssClass="old-asp-way success"
response.WriteLine("	<div class=""success""></div>")
response.WriteLine('	<div class=''whatever success something''></div>')

// Don't match these
class="text-success"
class="success-something"