Regular expressions match html characters to filter illegal characters

Match an html tag. The matching table is as follows:

<Table. *?> [Ss] * </table>
Or
<Table. *?> [Ss] *? </Table>

The above two expressions add "? "And one "? ", What is the difference?
We know "? "In a regular expression is a wildcard: matches the previous subexpression zero or once, or specifies a non-greedy qualifier.

Here, through testing, we come to the conclusion that "?" is not added "? When the following content is matched:

<Table> This is the first table. </table>
I am not the content in the table
<Table> This is the second table. </table>
I am not the content in the table either.
<Table> This is the third table. </table>

<?

$ Str = preg_replace ("/s +/", "", $ str); // filter excess carriage return
$ Str = preg_replace ("/<[] +/si", "<", $ str); // filter <__( "<" followed by a space)

$ Str = preg_replace ("/<! --.*? -->/Si "," ", $ str); // comment
$ Str = preg_replace ("/<(!. *?)> /Si "," ", $ str); // filter doctype
$ Str = preg_replace ("/<(/? Html. *?)> /Si "," ", $ str); // filter html tags
$ Str = preg_replace ("/<(/? Head. *?)> /Si "," ", $ str); // filter head tags
$ Str = preg_replace ("/<(/? Meta. *?)> /Si "," ", $ str); // filter meta Tags
$ Str = preg_replace ("/<(/? Body. *?)> /Si "," ", $ str); // filter the body tag
$ Str = preg_replace ("/<(/? Link. *?)> /Si "," ", $ str); // filter link tags
$ Str = preg_replace ("/<(/? Form. *?)> /Si "," ", $ str); // filter form labels
$ Str = preg_replace ("/cookie/si", "cookie", $ str); // filter cookie tags

$ Str = preg_replace ("/<(applet. *?)> (.*?) <(/Applet. *?)> /Si "," ", $ str); // filter the applet tag
$ Str = preg_replace ("/<(/? Applet. *?)> /Si "," ", $ str); // filter the applet tag

$ Str = preg_replace ("/<(style. *?)> (.*?) <(/Style. *?)> /Si "," ", $ str); // filter style labels
$ Str = preg_replace ("/<(/? Style. *?)> /Si "," ", $ str); // filter style labels

$ Str = preg_replace ("/<(title. *?)> (.*?) <(/Title. *?)> /Si "," ", $ str); // filter the title tag
$ Str = preg_replace ("/<(/? Title. *?)> /Si "," ", $ str); // filter the title tag

$ Str = preg_replace ("/<(object. *?)> (.*?) <(/Object. *?)> /Si "," ", $ str); // filter object tags
$ Str = preg_replace ("/<(/? Objec. *?)> /Si "," ", $ str); // filter object tags

$ Str = preg_replace ("/<(noframes. *?)> (.*?) <(/Noframes. *?)> /Si "," ", $ str); // filter noframes tags
$ Str = preg_replace ("/<(/? Noframes. *?)> /Si "," ", $ str); // filter noframes tags

$ Str = preg_replace ("/<(I? Frame. *?)> (.*?) <(/I? Frame. *?)> /Si "," ", $ str); // filter frame labels
$ Str = preg_replace ("/<(/? I? Frame. *?)> /Si "," ", $ str); // filter frame labels

$ Str = preg_replace ("/<(script. *?)> (.*?) <(/Script. *?)> /Si "," ", $ str); // filter script tags
$ Str = preg_replace ("/<(/? Script. *?)> /Si "," ", $ str); // filter script tags
$ Str = preg_replace ("/webpage effects/si", "javascript", $ str); // filter script tags
$ Str = preg_replace ("/vbscript/si", "vbscript", $ str); // filter script tags
$ Str = preg_replace ("/on ([a-z] +) s * =/si", "on \ 1 =", $ str); // filter script tags
$ Str = preg_replace ("// & #/si", "& #", $ str); // filter script tags, such as javascript: alert ('aabb)

?>