Sgml 中规定的特殊字符

* Use & for the ampersand (&),
* Use &lt; for a left bracket (<),
* Use &gt; for a right bracket (>),
* Use &lt;/ for a left bracket with a slash (</)
* Use &dollar; for a dollar sign ($),
* Use &num; for a hash (#),
* Use &percnt; for a percent (%),
* Use &tilde; for a tilde (~),
* Use `` and '' for quotes, or use &ldquo; for ``, &rdquo; for ''.