Context
j:parse provides a way to process a Jelly block and put the outcome in a variable
st:ajunct provides a way for developer to inject js/css (and other) resources into the page (with guarantee they are provided only once)

Problem
When trying to do a st:adjunct from within the j:parse, there is no effect. Actually the script is written to the textBuffer of the output instead of the XML output (as elements). When the output is transformed into String to be put in the variable, the textBuffer is not used.

Root cause
Adjunct#write use out.write instead of startElement/endElement.

Full details with screenshots: https://github.com/jenkinsci/jenkins/pull/5515#pullrequestreview-667429063