Học biểu thức chính qui trong php

My Code:
Pattern    Usage
>foo    The string "foo"
^foo    "foo" at the start of a string
foo$    "foo" at the end of a string
^foo$    "foo" when it is alone on a string
[abc]    a, b, or c
[a-z]    Any lowercase letter
[^A-Z]    Any character that is not a uppercase letter
(gif|jpg)    Matches either "gif" or "jpeg"
[a-z]+    One or more lowercase letters
[0-9\.\-    ] Аny number, dot, or minus sign
^[a-zA-Z0-9_]{1,}$     Any word of at least one letter, number or _
([wx])([yz])    wy, wz, xy, or xz
[^A-Za-z0-9]    Any symbol (not a number or a letter)
([A-Z]{3}|[0-9]{4})    Matches three letters or four numbers 
Special Sequences

    \w - Any “word” character (a-z 0-9 _)
    \W - Any non “word” character
    \s - Whitespace (space, tab CRLF)
    \S - Any non whitepsace character
    \d - Digits (0-9)
    \D - Any non digit character
    . - (Period) – Any character except newline

Meta Characters

    ^ - Start of subject (or line in multiline mode)
    $ - End of subject (or line in multiline mode)
    [ - Start character class definition
    ] - End character class definition
    | - Alternates, eg (a|b) matches a or b
    ( - Start subpattern
    ) - End subpattern
    \ - Escape character

Quantifiers

    n* - Zero or more of n
    n+ - One or more of n
    n? - Zero or one occurrences of n
    {n} - n occurrences exactly
    {n,} - At least n occurrences
    {n,m} - Between n and m occurrences (inclusive)

Pattern Modifiers

    i - Case Insensitive
    m - Multiline mode - ^ and $ match start and end of lines
    s - Dotall - . class includes newline
    x - Extended– comments and whitespace
    e - preg_replace only – enables evaluation of replacement as PHP code
    S - Extra analysis of pattern
    U - Pattern is ungreedy
    u - Pattern is treated as UTF-8

Point based assertions

    \b - Word boundary
    \B - Not a word boundary
    \A - Start of subject
    \Z - End of subject or newline at end
    \z - End of subject
    \G - First matching position in subject

Assertions

    (?=) - Positive look ahead assertion foo(?=bar) matches foo when followed by bar
    (?!) - Negative look ahead assertion foo(?!bar) matches foo when not followed by bar
    (?<=) - Positive look behind assertion (?<=foo)bar matches bar when preceded by foo
    (?<!) - Negative look behind assertion (?) - Once-only subpatterns (?>\d+)bar Performance enhancing when bar not present
    (?(x)) - Conditional subpatterns
    (?(3)foo|fu)bar - Matches foo if 3rd subpattern has matched, fu if not
    (?#) - Comment (?# Pattern does x y or z)

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