i match upper and lower case
Dot metacharacter (.) in s pattern matches all characters, including newlines
The whitespace characters in the x pattern are completely ignored except for escaped or in the character class. All characters, including both headers, between # except the unescaped character class, and between the next newline character, including both headers, are also ignored.
A (PCRE_ANCHORED) If this correction is set, the pattern is forced to "anchored", that is, it is forced to match only from the beginning of the target string, that is, it is automatically added to the beginning of the pattern.
D (PCRE_DOLLAR_ENDONLY) If this correction is set, the dollar dollar characters in the pattern only match the end of the target string. Without this option, if the last character is a newline, the dollar sign will also match before this character (but will not match any other newline). This option is ignored if the m correction symbol is set. There is no equivalent modifier in Perl. S When a pattern will be used several times, it is worth analyzing it for the sake of accelerating the matching. If this correction is set, additional analysis will be performed. Currently, analyzing a pattern is only useful for non-anchored patterns without a single fixed start character.
U (PCRE_UNGREEDY) This correction character reverses the value of the match number so that it is not the default duplication, but becomes followed by "?" before becoming duplicate. This is incompatible with Perl. This option can also be enabled by setting the (?U) modifier in mode.
X (PCRE_EXTRA) This modifier enables an additional feature in PCRE that is incompatible with Perl. Any backslash in the pattern followed by a letter with no special meaning causes an error, thus retaining this combination for further expansion. By default, like Perl, a backslash followed by a letter with no special meaning is regarded as the letter itself. No other features are currently controlled by this correction character. That is: greedy mode, maximum matching. For example: /a[\w]+?e/U matches abceade in abceadedddd instead of abce. If U is not corrected, it matches abce u (PCRE_UTF8). This correction character enables an additional function in PCRE that is incompatible with Perl. The pattern string is treated as UTF-8. This correction is available in Unix since PHP 4.1.0 and in win32 since PHP 4.2.3.
Dot metacharacter (.) in s pattern matches all characters, including newlines
The whitespace characters in the x pattern are completely ignored except for escaped or in the character class. All characters, including both headers, between # except the unescaped character class, and between the next newline character, including both headers, are also ignored.
A (PCRE_ANCHORED) If this correction is set, the pattern is forced to "anchored", that is, it is forced to match only from the beginning of the target string, that is, it is automatically added to the beginning of the pattern.
D (PCRE_DOLLAR_ENDONLY) If this correction is set, the dollar dollar characters in the pattern only match the end of the target string. Without this option, if the last character is a newline, the dollar sign will also match before this character (but will not match any other newline). This option is ignored if the m correction symbol is set. There is no equivalent modifier in Perl. S When a pattern will be used several times, it is worth analyzing it for the sake of accelerating the matching. If this correction is set, additional analysis will be performed. Currently, analyzing a pattern is only useful for non-anchored patterns without a single fixed start character.
U (PCRE_UNGREEDY) This correction character reverses the value of the match number so that it is not the default duplication, but becomes followed by "?" before becoming duplicate. This is incompatible with Perl. This option can also be enabled by setting the (?U) modifier in mode.
X (PCRE_EXTRA) This modifier enables an additional feature in PCRE that is incompatible with Perl. Any backslash in the pattern followed by a letter with no special meaning causes an error, thus retaining this combination for further expansion. By default, like Perl, a backslash followed by a letter with no special meaning is regarded as the letter itself. No other features are currently controlled by this correction character. That is: greedy mode, maximum matching. For example: /a[\w]+?e/U matches abceade in abceadedddd instead of abce. If U is not corrected, it matches abce u (PCRE_UTF8). This correction character enables an additional function in PCRE that is incompatible with Perl. The pattern string is treated as UTF-8. This correction is available in Unix since PHP 4.1.0 and in win32 since PHP 4.2.3.