(PHP 4, PHP 5, PHP 7)
imap_listscan — Returns the list of mailboxes that matches the given text
$imap_stream
   , string $ref
   , string $pattern
   , string $content
   ) : array
   Returns an array containing the names of the mailboxes that have
   content in the text of the mailbox.
  
   This function is similar to imap_listmailbox(),
   but it will additionally check for the presence of the string
   content inside the mailbox data.
  
imap_stream由 imap_open() 返回的 IMAP 流。
ref
       ref should normally be just the server 
       specification as described in imap_open()
      
Passing untrusted data to this parameter is insecure, unless imap.enable_insecure_rsh is disabled.
pattern指定在邮箱层级的何处开始查找。
在组成 pattern 的字符中可使用两个特殊字符:
 '*' 和 '%'。
 '*' 是指返回所有邮箱目录. 如果将 '*' 作为
 pattern 参数时, 则会返回整个邮箱层级结构。
 '%' 是指只返回当前级次。
 '%' 作为 pattern 参数则只会返回顶层邮箱;
 '~/mail/%' 用于 UW_IMAPD
 则会返回名为 ~/mail 的目录, 但不包含其子目录。
contentThe searched string
   Returns an array containing the names of the mailboxes that have
   content in the text of the mailbox.