Regular Expressions 101

Group header_all(?<header_all> (?<!\\) # Make sure this is not escaped (?<header_level>\#+) # one or more # [ \t]* # Possibly followed by some spaces or tabs (?<header_content>.+?) # Header content enclosed [ \t\#]* # Possibly followed by some spaces or tabs or some dashes (don't need to match the opening ones) \n+ # Terminated by a new line )

Negative Lookbehind(?<!\\)

\\the literal \ (92₁₀ / 134₈ / 5C₁₆)

Comment: Make sure this is not escaped

Group header_level(?<header_level>\#+)

\#+the literal # (35₁₀ / 43₈ / 23₁₆) , repeated at least once

Comment: one or more #

Character Class[ \t]*

*matches any number of characters from the set below:

the literal (32₁₀ / 40₈ / 20₁₆)

\ta tab character (ASCII 9)

Comment: Possibly followed by some spaces or tabs

Group header_content(?<header_content>.+?)

.+?any character (except for line terminators), repeated at least once

Comment: Header content enclosed

Character Class[ \t\#]*

*matches any number of characters from the set below:

the literal (32₁₀ / 40₈ / 20₁₆)

\ta tab character (ASCII 9)

\#the literal # (35₁₀ / 43₈ / 23₁₆)

Comment: Possibly followed by some spaces or tabs or some dashes (don't need to match the opening ones)

\n+a line-feed (newline) character (ASCII 10), repeated at least once

Comment: Terminated by a new 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

x modifier: extended. Ignores unescaped whitespace and comments outside character classes

Detailed match information will be displayed here automatically.

25 tokens

Regular Expression

(?<header_all>
    (?<!\\)                     # Make sure this is not escaped
    (?<header_level>\#+)        # one or more #
    [ \t]*                      # Possibly followed by some spaces or tabs
    (?<header_content>.+?)      # Header content enclosed
    [ \t\#]*                    # Possibly followed by some spaces or tabs or some dashes (don't need to match the opening ones)
    \n+                         # Terminated by a new line
)

New

### Header
Paragraph

#### Header ##

Substitution

### Header
Paragraph

#### Header ##