Question

First, the way I understand it, it’s more appropriate to use numeric entities in an XHTML document, such as " instead of ", is that right?

Second, for my RSS XML feed, which entity type is correct? Named or numeric? I believe it’s numeric, but see examples of both in my searches.

Third, which of the following is correct for entities inside inline JavaScript?

<span onmouseover="tooltip_on( '<strong>Tooltip inside a span</strong>
<br />Lorem ipsum dolor sit amet.<span>Lorem ipsum <code>dolor sit</code>
amet, consectetur adipisicing elit.</span>' );"
onmouseout="tooltip_off();">tooltip inside a span</span>

OR… (the tags inside the JS function are converted to named entities):

<span onmouseover="tooltip_on( '&lt;strong&gt;Tooltip inside a
span&lt;/strong&gt;&lt;br /&gt;Lorem ipsum dolor sit amet.
&lt;span&gt;Lorem ipsum &lt;code&gt;dolor sit&lt;/code&gt;
amet, consectetur adipisicing elit.&lt;/span&gt;' );"
onmouseout="tooltip_off();">tooltip inside a span</span>

EDIT 1:

Great answers below, but maybe I should have worded my question differently.

Disregarding the JavaScript question, which would YOU use for YOUR website and RSS feed:

(1) All numeric entities, (2) all named entities, (3) a mixture of both: & " < >, with the rest being numeric.

I am leaning towards 3 because my site already has & " < > ' deeply embedded, plus htmlspecialchars() used in quite a few places.

EDIT 2:

All good answers below, folks. Had to pick just one, unfortunately.

Answer 1

First, the way I understand it, it’s more appropriate to use numeric entities in an XHTML document, such as " instead of ", is that right?

" is also defined for XHTML. So you can use both.

Second, for my RSS XML feed, which entity type is correct? Named or numeric? I believe it’s numeric, but see examples of both in my searches.

Again, " is also defined for XML. So you can use both.

Third, which of the following is correct for entities inside inline JavaScript?

The second one is correct since a plain < is not allowed inside an attribute value declaration (but > is).

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Edit    Now that you refined your question:

I would use a charset that contains all characters I need. So if you want to be able to use almost any character, use Unicode and encode the characters with UTF-8.

Thereby you can encode any character with UTF-8 directly and have no need to use character references for characters other than the special characters of XML (at least &, >, " and ').

And here you have the free choice between the named or numeric character references. Use what you like better or what your programming language uses/prefers.