What determines if a field can be edited inline?

1) Mainline fields only, no subrecords (including address/item lines/expenses etc.) 2) Field must be enabled in default form for record type 3) I think* multiselect fields often have problems. 4) Field sourcing must be turned off. 5) Field filtering may/may not work. (native filter will, custom fields filtering won't generally) 6) I think there's a suite answers article on this, but not inclined to go digging for it.

@KevinJ of Kansas Thanks. I see now why the field i wanted to edit inline I cannot (#4 Field Sourcing).