<?php 
    /**
     * author: goosman
     * blog: http://blog.csdn.net/lgg201
     * mail: [email protected]
     */ 

    $str    = '0123456789<a>012</a>0123456789'; 
    function substr_remain_tag($s, $o, $l) { 
        $is_match   = preg_match_all(<<<heredoc 

    # The regular expression is parsed xml The label ,  Escape characters are supported inside tag properties "\",  Support for "\" The escape of itself and the corresponding quotation marks  
    <(\w+)             # Tags start  
        (?:          # Property list  
            \s+       # Leading Spaces  
            \w+    # The property name
            \s*    # White space after the property name ( In order to compatible ) 
            =        # Equal sign between property name values  
            \s*       # White space before property values ( In order to compatible ) 
            (?:         # Attribute values ( Quotes processing ) 
                "         # Double quotation marks  
                (?: 
                    \\\\\\\\   # Eat two escape characters in a row ( Represents the escape character itself ) 

                    \\\\"          # Eat the escape character next 1 The quotation ( Quotation marks for escape ) 

                    [^"\\\\]*   # Other characters  
                )* 
                " 

                '       # Single quotation mark case  
                (?: 
                    \\\\\\\\   # Eat two escape characters in a row ( Represents the escape character itself ) 

                    \\\\'   # Eat the escape character next 1 The quotation ( Quotation marks for escape ) 

                    [^'\\\\]*       # Other characters  
                )* 
                ' 
            ) 
        )* 
    > 
    .*?               # Label content  
    </(?1)>     # End tag  
    ;x 
    heredoc 
    , $s, $matches, PREG_OFFSET_CAPTURE, $o); 
        if ( $is_match ) { 
            foreach ( $matches[0] as $match ) { 
                $o0 = $match[1]; 
                # The left edge of the tag crosses the right edge of the intercept target ,  exit  
                if ( $o0 >= $o + $l ) break; 
                $l0 = strlen($match[0]); 
                # The right border of the tag is inside the right border of the interception target ,  Continue to  
                if ( $o0 + $l0 < $o + $l ) continue; 

                # The following is the label transboundary processing  
                $l  = $o0 + $l0 - $o; 
                break; 
            } 
        } 
        return substr($s, $o, $l); 
    }  
    echo $str . chr(10); 
    echo substr_remain_tag($str, 0, 20) . chr(10);