Regular Expressions 101

Explanation

Pro

^start of line

Non-Capturing Group(?:(?:>|<(?!.*<))?[a-zA-Z]+(?:(?:\+|-)\d*\.?\d*(?:em)?)?)

Non-Capturing Group(?:>|<(?!.*<))?

?repeats the group contents below at most once:

1st Alternative>

>the literal > (62₁₀ / 76₈ / 3E₁₆)

2nd Alternative<(?!.*<)

<the literal < (60₁₀ / 74₈ / 3C₁₆)

Negative Lookahead(?!.*<)

.*any character (except for line terminators), repeated any number of times

<the literal < (60₁₀ / 74₈ / 3C₁₆)

Character Class[a-zA-Z]+

+matches at least one character from the set below:

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

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

Non-Capturing Group(?:(?:\+|-)\d*\.?\d*(?:em)?)?

?repeats the group contents below at most once:

Non-Capturing Group(?:\+|-)

1st Alternative\+

\+the literal + (43₁₀ / 53₈ / 2B₁₆)

2nd Alternative-

-the literal - (45₁₀ / 55₈ / 2D₁₆)

\d*a digit, repeated any number of times

\.?optionally matches the literal . (46₁₀ / 56₈ / 2E₁₆)

\d*a digit, repeated any number of times

Non-Capturing Group(?:em)?

?repeats the group contents below at most once:

emthe literal text em (case sensitive)

Non-Capturing Group(?:<?[a-zA-Z]+(?:(?:\+|-)\d*\.?\d*(?:em)?)?)?

?repeats the group contents below at most once:

<?optionally matches the literal < (60₁₀ / 74₈ / 3C₁₆)

Character Class[a-zA-Z]+

+matches at least one character from the set below:

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

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

Non-Capturing Group(?:(?:\+|-)\d*\.?\d*(?:em)?)?

?repeats the group contents below at most once:

Non-Capturing Group(?:\+|-)

1st Alternative\+

\+the literal + (43₁₀ / 53₈ / 2B₁₆)

2nd Alternative-

-the literal - (45₁₀ / 55₈ / 2D₁₆)

\d*a digit, repeated any number of times

\.?optionally matches the literal . (46₁₀ / 56₈ / 2E₁₆)

\d*a digit, repeated any number of times

Non-Capturing Group(?:em)?

?repeats the group contents below at most once:

emthe literal text em (case sensitive)

$end of line

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

Unit Test Summary

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Quick Reference

26 tokens

Regular Expression

^(?:(?:>|<(?!.*<))?[a-zA-Z]+(?:(?:\+|-)\d*\.?\d*(?:em)?)?)(?:<?[a-zA-Z]+(?:(?:\+|-)\d*\.?\d*(?:em)?)?)?$

Unit Tests

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