Great, many thanks, that's exactly what I meant.

However, on trying it out, I found that any
newlines and indentation within my <block>
element contribute to the string_length, so that
my <block> is no longer 1 character long when they are present.

Ah, then your statement "all the text in my
<block> elements is found in child <inline> elements" is misleading.

So I would like to ask again, but this time: how
to match any <block> in which the sum of the
lengths of the child <inline> elements is 1
character? (My newlines and indentation will be
outside any <inline> element, but all the
"content" is inside <inline> elements.)  Do I
need to program a loop somehow, or is there a handy function?

I like Piet's idea of declaring that the
white-space children of the <block> element are
considered throw-away indentation and not information:

If you really wanted an algorithmic way, then
something along the lines of the following in XSLT 2 would work:

 <xsl:template match="block[sum(for $each in
inline return string-length($each))
                            =1]">
   ...
 </xsl:template>

... which is nicely abbreviated by Piet's
suggestion of joining all of the inlines and
calculating the length of the join.

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