[xsl] Optimizing preceding-sibling & following-sibling axes (with key()?)

[Martynas Jusevicius <martynas.jusevicius@xxxxxxxxx>]

Hey,

I have such a variable definition (quite cumbersome):

<xsl:variable name="descendant-headings"
select="following-sibling::h:*[self::h:h1 or self::h:h2 or self::h:h3
or self::h:h4 or self::h:h5 or self::h:h6][o2e:heading-level(.) &gt;
o2e:heading-level(current())][preceding-sibling::h:*[self::h:h1 or
self::h:h2 or self::h:h3 or self::h:h4 or self::h:h5 or
self::h:h6][o2e:heading-level(.) = o2e:heading-level(current())][1] is
current()]"/>

Basically, I need to select all descendant (level-wise, not as in
descendant axis) headings for the current() one, meaning all following
headings with lower level which go before the next heading one the
same level as current(). This expression gives me what I need.
o2e:heading-level() function simply extracts the level number from
elements name, like 'h3'.

Now, I've read multiple times that preceding-sibling/following-sibling
are slow. I wonder if this expression could be optimized?
I also have a key definition which I use for similar purposes:

<xsl:key name="heading-by-level" match="h:h1 | h:h2 | h:h3 | h:h4 |
h:h5 | h:h6" use="number(substring-after(local-name(), 'h'))"/>

I just can't figure out how combine this key with the sibling axes to
get the same result and improve performance, i.e. that instead of
traversing the whole document it would be enough to traverse key()
values, like in key('heading-by-level', 1 to 6).
Does it make sense?

Thanks,

Martynas
odt2epub.com