more work on documenting residual similarities with C64 KERNAL

strings/A9003860

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+LDA #$00 / SEC / RTS - Return failure and 0 from a KERNAL routine
+
+The C64 KERNAL public API indicates that the carry flag should be set
+to report failure of many routines, and those routines can also return
+A=$00 as part of that.  
+Also, returning such values from a routine is not uncommon generally,
+and lacks all creativity. Not copyrightable.
+
+