The concept of modes and mode selection is common in the kinds of applications I draft and prosecute. Modes are almost always mutually exclusive, so the system is in one of the supported modes at a time. Therefore, using "or" when describing mode behavior seems natural to me, and I would interpret the above limitation as a button that selects between the two modes.
The Board's footnote in Nguyen suggests that the Board would interpret this limitation differently:
We note that the "single button" of claim 1 also reads on a button that merely selects either a write mode or pan mode, i.e., not necessarily both.I read this as "a button that selects write mode reads on the claimed button; a button that selects pan mode reads on this button; the button doesn't have to toggle between the two." Whereas my interpretation of the claimed button does require the button to toggle between the two.
This is the first Board decision I recall that suggested this interpretation, but I've definitely run across Examiners who treat the phrase "X or Y" as permission to find only one of them in the reference. You can try to convince the Examiner (or the Board) that "or" doesn't always have such a narrow meaning, but I think this claim language might work better: "a single button for controlling said means for operating to allow a said user to select BETWEEN said write mode AND said pan mode."
One weakness I can see with my proposed claim language is this: what if there modes other than write and pan? Will the accused infringer attempt to argue that your claim requires switching between exactly these two modes?