Regular Expressions 101

Explanation
Pro

Negative Lookahead(?!^)

^start of line

Negative Lookbehind(?<!\bNo\.\s)

\ba Unicode word boundary

Nothe literal text No (case sensitive)

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

\sa Unicode whitespace character

Negative Lookbehind(?<!\bQuestion\s)

\ba Unicode word boundary

Questionthe literal text Question (case sensitive)

\sa Unicode whitespace character

Negative Lookbehind(?<!\d)

\da Unicode decimal digit

Negative Lookahead(?!(?:19[6-9][0-9]|20[01][0-9]|2020)(?!\d))

Non-Capturing Group(?:19[6-9][0-9]|20[01][0-9]|2020)

1st Alternative19[6-9][0-9]

19the literal text 19

Character Class[6-9]

6-9one character from 6 (54₁₀) to 9 (57₁₀)

Character Class[0-9]

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

2nd Alternative20[01][0-9]

20the literal text 20

Character Class[01]

0the literal 0 (48₁₀ / 60₈ / 30₁₆)

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

Character Class[0-9]

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

3rd Alternative2020

2020the literal text 2020

Negative Lookahead(?!\d)

\da Unicode decimal digit

Group 1(\d+(?!\d)e?)

\d+a Unicode decimal digit, repeated at least once

Negative Lookahead(?!\d)

\da Unicode decimal digit

e?optionally matches the literal e (101₁₀ / 145₈ / 65₁₆) (case sensitive)

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

25 tokens

Regular Expression

(?!^)(?<!\bNo\.\s)(?<!\bQuestion\s)(?<!\d)(?!(?:19[6-9][0-9]|20[01][0-9]|2020)(?!\d))(\d+(?!\d)e?)

Unit Tests

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