[xsl] template match question

[Ciarán Ó Duibhín <ciaran@xxxxxxxxxxxxxxxxxxxxxxxx>]

Please excuse a specific and elementary query on XSL.

I understand how

  <xsl:template match="block[string-length(./inline)=1]">

matches any <block> element which has as child an <inline> element whose 
text content is one character in length.

But how can I change this to match any <block>, for which the sum of the 
lengths of its <inline> child elements is one character; or alternatively, 
any <block> the length of whose whole text content is1 character, since all 
the text in my <block> elements is found in child <inline> elements?

Many thanks,
Ciaran S Duibhmn