New line in cursor-intangible area and line-beginning position

Question

I want to make the beginning of a line uneditable, which I can achieve by applying the read-only and cursor-intangible properties. But I have the problem, that line-beginning-position moves point not to the first reachable position of the current line, as I expect, but to the end of the previous line. This may be a bug in Emacs. Is there some workaround for this issue?

Example: Let's say buffer contains "blablabla\nINTANGIBLEfooooo" INTANGIBLE has properties cursor-intangible t rear-nonsticky t front-sticky t. Then it is not possible to put point before any symbol of "INTANGIBLE", that is exactly wanted behavior, however if point is somewhere in fooooo, move-beginning-of-line puts point to the end of blablabla, which is strange.

Reconstruction:

• Copy and paste the following form into the *scratch* buffer. There the black rectangle ▮ indicates the point position. (You should not copy that character.)

(insert "\nblablabla\n"
        (propertize "INTANGIBLE" 'cursor-intangible t 'rear-nonsticky t 'front-sticky t)
        "fooooo")▮

• Eval the form with C-x C-e. You get

(insert "\nblablabla\n"
        (propertize "INTANGIBLE" 'cursor-intangible t 'rear-nonsticky t 'front-sticky t)
        "fooooo")
blablabla
INTANGIBLEfooooo▮

• Hit the home key. You end up with:

(insert "\nblablabla\n" (propertize "INTANGIBLE" 'cursor-intangible t 'rear-nonsticky t 'front-sticky t) "fooooo")
blablabla▮
INTANGIBLEfooooo

---

It becomes really interesting if one tries to get this behavior completely with the evaluation of a lisp expression:

(progn
  (insert "\nblablabla\n"
          (propertize "INTANGIBLE" 'cursor-intangible t 'rear-nonsticky t 'front-sticky t)
          "fooooo")
  (call-interactively #'move-beginning-of-line))▮

After evaluation with C-x C-e one gets:

I.e., point is between the last intangentiable character and the f of foooooo.

Answer 1

Applying field property to intangible area solves the problem.

Adding of field t to the properties of INTANGIBLE makes move-beginning-of-line putting point between INTANGIBLE and fooooo, like expected.

Reconstruction:

• Copy-paste following lisp code into the *scratch* buffer. There the black rectangle ▮ indicates the point position. (You should not copy that character.)

(insert "\nblablabla\n"
        (propertize "INTANGIBLE"
                    'cursor-intangible t
                    'rear-nonsticky t
                    'front-sticky t
                    'field t)
        "fooooo")▮

• Evaluate it with C-x C-e.
• Press the home key. You get:

I.e., point is between the last intangentiable character and the f of foooooo.