Regular Expressions 101

Explanation

Pro

Non-Capturing Group(?:^|\n)

1st Alternative^

^start of line

2nd Alternative\n

\na line-feed (newline) character (ASCII 10)

Group 1(([0-9]+)\.[\s\S]*?)

Group 2([0-9]+)

Character Class[0-9]+

+matches at least one character from the set below:

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

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

Character Class[\s\S]*?

*?matches any number of characters from the set below:

\sa Unicode whitespace character

\Sany character that is not Unicode whitespace

Positive Lookahead(?=\n[0-9]+\.|\Z)

1st Alternative\n[0-9]+\.

\na line-feed (newline) character (ASCII 10)

Character Class[0-9]+

+matches at least one character from the set below:

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

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

2nd Alternative\Z

\Zend of string

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

Detailed match information will be displayed here automatically.

25 tokens

(?:^|\n)(([0-9]+)\.[\s\S]*?)(?=\n[0-9]+\.|\Z)

New

1. First sentence. 
2. Second sentence. 
1. Another sentence. 
3. Third sentence.

1. First sentence. 
2. Second sentence. 
1. Another sentence. 
3. Third sentence.