Alternative to @falsetru's answer
(By "trying to read the version tag", I understand "the version attribute" (which may not be what you want))
Explicitly register fvdl namespace, under the "fvdl" prefix:
ver = context.xpath('//fvdl:FVDL/@version',
namespaces={"fvdl": "xmlns://www.fortifysoftware.com/schema/fvdl"})
Or, riskier, if somehow you know you want the version
attribute from the root node
ver = context.xpath('/*/@version')
Both give ['1.9']