Huge history as I can see.
Again in XHTML 1.1 none of the mandatory child element of the
<head> tag support a
Then I may suggest 2 workarounds :
First one : to cycle manually through meta tags until the one which attribute
syntaxhighlighter-version is found. There we can insert
themecss just before.
Second one : to do the same but using WordPress's internal jQuery to catch the correct tag using a direct selector, that would look like :
Both solutions may imply a loss of performance during the script load, but negligible I assume.