Actually, it’s more complicated than that. For XHTML, all you need is <![CDATA[ and ]]>. However, typical HTML parsers don’t understand <![CDATA[ and will throw an error if it is inside a script or style element. So we have to resort to a hack:
starting line: <!–//–><![CDATA[//><!–
ending line: //–><!]]>
This is how it works:
Remember how HTML parsers ignore the first line in a script element if it starts with “<!–”? That would prevent HTML parsers from seeing the “<![CDATA[”. However, that type of trick doesn’t work in XHTML and would in fact prevent the script from being executed. So we need to end the comment (“–>”) before the “<![CDATA[”, but if we do that, than the “<![CDATA[” would no longer be hidden to some HTML parsers. So inside the comment, we add “//” that the XHTML parser will ignore (since it really ignores everything inside comments) and most HTML parsers will allow their JS parsers to comment out the rest of the line, including the “<![CDATA[”.
So: <!–//–><![CDATA[
Most modern browsers would actually work with just “<!-- –>”, since the “<!–” itself would comment out the whole line, but not all HTML parsers are like that.
But what about legacy browsers that don’t support Javascript? In this case, the goal is to make sure the script internals aren’t displayed. Since they don’t support the “<!–” whole line commenting, the “<![CDATA[” is again visible. Next trick: turn the “<![CDATA[” into a “processing instruction” tag (<!foo>), which won’t be recognized nor outputted. “<![CDATA[>” would hide it from legacy browsers. However, it wouldn’t work with XHTML, since it would consider the “>” to be the first character of the script. So replace that with “//>” so it would ignore that “>” and the rest of the line: “<![CDATA[//>”. Finally, add the “<!–” to the end to hide the rest of the script from legacy browsers.
So: <!–//–><![CDATA[//><!–
The ending part goes along the same lines. XHTML parsers needs the “]]>”, but HTML parsers don’t understand that (and the JS parser would throw an error). So that needs to be commented out with “//”.
So: //]]>
Now to support legacy browsers. They need “–>” somewhere. It can’t go after the “]]>” since the XHTML parser will see an comment end without a comment start. That could be solved by using the “<!-- –>” trick, but there’s a more elegant solution. Add the “–>” before the “]]>” and make the “]]>” into a processing instruction tag to hide it: “–><!]]>”. Also, the “<!-- –>” would actually fail for a fully compliant HTML parser that doesn’t support JS since its actually the “–” that toggles off/on comments, not the “<!–”/“–>”, and the whole comment would be like: “<!-- …script stuff here… //]]><!-- –>”, which has 3 “–”'s. However, to avoid going into that esoteric stuff, just stick with “–><!]]>”.
So: //–><!]]>