Text property 'intangible and fontification

[Lennart Borgman (gmail)]

I think I noticed a problem with nxml-mode (not part of Emacs) and 
fontification when an overlay has the property 'intangible. I am not 
sure about what happens, but I believe that when such an overlay is over 
text that nxml-mode wants to fontify then it fails and restarts again. 
Emacs then grabs 99% of the CPU.

nxml-mode does its own fontification since it anyway parses the buffer 
contents. What should fontification code do when there are some overlays 
like this? Or text properties. Should it let bind 
`inhibit-point-motion-hooks' to t, or? What does other fontification 
code do in Emacs?