The following XPath functions are currently not supported, but can be implemented using
Tamino server extensions, as long as they do not have a variable number of arguments:
concat
contains
id
lang
local-name
namespace-uri
normalize-space
string-length
substring
substring-after
substring-before
translate
under doc type def, you can apply transformation, just wrap a substring function under your transformation service, then you will get whatever you want.