Regular Expressions 101

Explanation

Pro

Non-Capturing Group(?: \G(?!\A) # second entry point (?: # content up to the next alt/title attribute (optional) [^><"]* " # end of the previous attribute (?> [^><"]* " [^"]* " )*? # other attributes (optional) [^><"]* # spaces or attributes without values (optional) \b(?:alt|title)\s*=\s*" # the next alt/title attribute )?+ # make all the group optional | <img\s[^>]*?\b(?:alt|title)\s*=\s*" # first entry point )

1st Alternative \G(?!\A) # second entry point (?: # content up to the next alt/title attribute (optional) [^><"]* " # end of the previous attribute (?> [^><"]* " [^"]* " )*? # other attributes (optional) [^><"]* # spaces or attributes without values (optional) \b(?:alt|title)\s*=\s*" # the next alt/title attribute )?+ # make all the group optional

\Gstart of current search

Negative Lookahead(?!\A)

\Astart of string

Comment: second entry point

Non-Capturing Group(?: # content up to the next alt/title attribute (optional) [^><"]* " # end of the previous attribute (?> [^><"]* " [^"]* " )*? # other attributes (optional) [^><"]* # spaces or attributes without values (optional) \b(?:alt|title)\s*=\s*" # the next alt/title attribute )?+

?+repeats the group contents below at most once:

Comment: content up to the next alt/title attribute (optional)

Negated Character Class[^><"]*

*matches any number of characters outside the set below:

>the literal > (62₁₀ / 76₈ / 3E₁₆)

<the literal < (60₁₀ / 74₈ / 3C₁₆)

"the literal " (34₁₀ / 42₈ / 22₁₆)

" the literal text "

Comment: end of the previous attribute

Atomic Group(?> [^><"]* " [^"]* " )*?

*?repeats the group contents below any number of times:

Negated Character Class[^><"]*

*matches any number of characters outside the set below:

>the literal > (62₁₀ / 76₈ / 3E₁₆)

<the literal < (60₁₀ / 74₈ / 3C₁₆)

"the literal " (34₁₀ / 42₈ / 22₁₆)

" the literal text "

Negated Character Class[^"]*

*matches any number of characters outside the set below:

"the literal " (34₁₀ / 42₈ / 22₁₆)

" the literal text "

Comment: other attributes (optional)

Negated Character Class[^><"]*

*matches any number of characters outside the set below:

>the literal > (62₁₀ / 76₈ / 3E₁₆)

<the literal < (60₁₀ / 74₈ / 3C₁₆)

"the literal " (34₁₀ / 42₈ / 22₁₆)

Comment: spaces or attributes without values (optional)

\ban ASCII word boundary

Non-Capturing Group(?:alt|title)

1st Alternativealt

altthe literal text alt (case sensitive)

2nd Alternativetitle

titlethe literal text title (case sensitive)

\s*any whitespace character, repeated any number of times

=the literal = (61₁₀ / 75₈ / 3D₁₆)

\s*any whitespace character, repeated any number of times

" the literal text "

Comment: the next alt/title attribute

Comment: make all the group optional

2nd Alternative <img\s[^>]*?\b(?:alt|title)\s*=\s*" # first entry point

<imgthe literal text <img (case sensitive)

\sany whitespace character

Negated Character Class[^>]*?

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

>the literal > (62₁₀ / 76₈ / 3E₁₆)

\ban ASCII word boundary

Non-Capturing Group(?:alt|title)

1st Alternativealt

altthe literal text alt (case sensitive)

2nd Alternativetitle

titlethe literal text title (case sensitive)

\s*any whitespace character, repeated any number of times

=the literal = (61₁₀ / 75₈ / 3D₁₆)

\s*any whitespace character, repeated any number of times

" the literal text "

Comment: first entry point

Negated Character Class[^<"]*+

*+matches any number of characters outside the set below:

<the literal < (60₁₀ / 74₈ / 3C₁₆)

"the literal " (34₁₀ / 42₈ / 22₁₆)

\Kresets the starting point of the reported match. Any previously consumed characters are no longer included in the final match

Non-Capturing Group(?: # two possibilities: </?a[^>]*> # an "a" tag (opening or closing) | # OR (?=") # followed by the closing quote )

1st Alternative # two possibilities: </?a[^>]*> # an "a" tag (opening or closing)

Comment: two possibilities:

<the literal text <

/?optionally matches the literal / (47₁₀ / 57₈ / 2F₁₆)

athe literal a (97₁₀ / 141₈ / 61₁₆) (case sensitive)

Negated Character Class[^>]*

*matches any number of characters outside the set below:

>the literal > (62₁₀ / 76₈ / 3E₁₆)

> the literal text >

Comment: an "a" tag (opening or closing)

2nd Alternative # OR (?=") # followed by the closing quote

Comment: OR

Positive Lookahead(?=")

"the literal " (34₁₀ / 42₈ / 22₁₆)

Comment: followed by the closing quote

Global pattern flags

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

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

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Quick Reference

25 tokens

Regular Expression

(?:
    \G(?!\A)                             # second entry point
    (?:                                    # content up to the next alt/title attribute (optional)
        [^><"]* "                             # end of the previous attribute
        (?> [^><"]* " [^"]* " )*?             # other attributes (optional)
        [^><"]*                               # spaces or attributes without values (optional)
        \b(?:alt|title)\s*=\s*"               # the next alt/title attribute
    )?+                                    # make all the group optional
  |
    <img\s[^>]*?\b(?:alt|title)\s*=\s*"  # first entry point
)
[^<"]*+\K
(?:              # two possibilities:
    </?a[^>]*>     # an "a" tag (opening or closing)
  |                # OR
    (?=")          # followed by the closing quote
)

Unit Tests

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