Let's say I have an org file with this content (this is the Org Manual):
*** System-wide header arguments #+vindex: org-babel-default-header-args
The file is opened normally, highlighted and everything.
Now, as a test I try to add a display property to the S character of System:
(put-text-property (point) (1+ (point)) 'display "aaa")
It works. The S is replaced with aaa.
But if I try the same on a character on the vindex line then nothing happens.
Why is that?