Regular Expressions 101

Explanation

Pro

Positive Lookahead(?=(?:[A-Za-z\.#\*]))

Non-Capturing Group(?:[A-Za-z\.#\*])

Character Class[A-Za-z\.#\*]

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

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

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

#the literal # (35₁₀ / 43₈ / 23₁₆)

\*the literal * (42₁₀ / 52₈ / 2A₁₆)

Group 1((?<=(?:[\s])|(?<=^)))

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

1st Alternative(?:[\s])

Non-Capturing Group(?:[\s])

Character Class[\s]

\sany whitespace character

2nd Alternative(?<=^)

Positive Lookbehind(?<=^)

^start of line

Character Class[a-z-\[\]:{1,2}#\.\*]+

+matches at least one character from the set below:

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

-the literal - (45₁₀ / 55₈ / 2D₁₆)

\[the literal [ (91₁₀ / 133₈ / 5B₁₆)

\]the literal ] (93₁₀ / 135₈ / 5D₁₆)

:the literal : (58₁₀ / 72₈ / 3A₁₆)

{the literal { (123₁₀ / 173₈ / 7B₁₆)

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

,the literal , (44₁₀ / 54₈ / 2C₁₆)

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

}the literal } (125₁₀ / 175₈ / 7D₁₆)

#the literal # (35₁₀ / 43₈ / 23₁₆)

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

\*the literal * (42₁₀ / 52₈ / 2A₁₆)

Group 2(\s+)?

?repeats the group contents below at most once:

\s+any whitespace character, repeated at least once

{the literal { (123₁₀ / 173₈ / 7B₁₆)

Global pattern flags

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

m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string

Match Information

Detailed match information will be displayed here automatically.

Quick Reference

25 tokens

Regular Expression

(?=(?:[A-Za-z\.#\*]))((?<=(?:[\s])|(?<=^)))[a-z-\[\]:{1,2}#\.\*]+(\s+)?{

New

custom {
}
custom {
}
custom-tag.lol {
}
custom-tag[lol] {
}
custom-tag:active {
}
custom-tag::after {
}
.lol {
	custom-tag {
	}
}

[a-z-\[\]:{1,2}#\.\*]+(\s+)?{
(?(?=\w) (?<!\w)  | (?<!\W) )

Substitution

custom {
}
custom {
}
custom-tag.lol {
}
custom-tag[lol] {
}
custom-tag:active {
}
custom-tag::after {
}
.lol {
	custom-tag {
	}
}

[a-z-\[\]:{1,2}#\.\*]+(\s+)?{
(?(?=\w) (?<!\w)  | (?<!\W) )