For ergonomic reasons, ALT is in a special location by itself just below the Play Speed control group. It, along with SHIFT and CTRL (Control) are what are termed ‘qualifiers buttons’, in that (like their keyboard equivalents) they qualify, or modify the outcome of operating some other control.
We’ve discussed one use of ALT in Section 21.6.6; see also Section 21.6.8. At the time of writing SHIFT and CTRL are reserved for as yet unspecified future purposes.
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