Google of "cad undercuts display"

An undercut is a design feature that interferes with the ejection of a molded part from the mold. An undercut can include features such as holes or boses that are not aligned with the direction of ejection, threaded sections, and snap fingers.

https://knowledge.autodesk.com/search-result/caas/CloudHelp/cloudhelp/2016/ENU/DFM/files/GUID-CCAB8DFA-9719-44C3-9C88-0C5A3185C148-htm.html#:~:text=An%20undercut%20is%20a%20design,threaded%20sections%2C%20and%20snap%20fingers.&text=The%20snap%20finger%20shown%20above%20has%20an%20undercut%20surface%20highlighted%20in%20red.

For a rotary shaft with an "undercut", a keyway,
this link has 3 good points:
1. Illustrate as a cross-section...
2. Never dimension to hidden lines.
3. The axis should be drawn so everyone can tell at a first glance. (Whatever that means?)
4. Dimension key cuts as a diameter of the shaft, from the bottom of the cut to the "other side" of the shaft, not as a depth of the cut.

https://www.reddit.com/r/AskEngineers/comments/fore6a/in_cad_drawings_is_it_common_practice_to_omit_the/

https://imgur.com/1UWrBiQ

https://knowledge.autodesk.com/search-result/caas/CloudHelp/cloudhelp/2016/ENU/DFM/files/GUID-CCAB8DFA-9719-44C3-9C88-0C5A3185C148-htm.html

https://www.aegisdentalnetwork.com/idt/2011/10/the-cad-in-cad-cam
"Just about all CAD programs today automatically block out undercuts with a click of a button or check of a checkbox."
(Expensive dental CAD)

https://www.protolabs.com/resources/blog/design-validation-with-solidworks-injection-molding/

- Brian (I have no personal knowledge on this subject. But learned a little bit...)