Bug report: ESC applied to attribute values produces spurious output

[Ron Garret]

? (with-html-output-to-string (s) ((:a :href (esc "XXX")) (esc "YYY")))
"<aXXX href='XXX'>YYY</a>"

My actual use case is:

(:a :onclick (esc "f('str')"))

This is CL-WHO 1.1.1 acquired through quicklisp.

rg