View source for Axis

* The Axis operator is allowed with all primitive scalar dyadic functions (e.g., <apll>1 2+[1] 2 3⍴R</apll>) and some scalar monadic functions (e.g., <apll>&lt;[1] 2 3⍴R</apll>)
* The Axis operator is allowed with some primitive operators (e.g., <apll>L←'abcdef' ⋄ R←⍳⍴L ⋄ L ,⍤[1] 0 R ←→ L,[0.5] R</apll>)
* The Axis operator to primitive scalar dyadic functions may transpose coordinates (e.g., <apll>(2 3⍴L)+[1 2] 2 3 4⍴R ←→ (⍉2 3⍴L)+[2 1] 2 3 4⍴R</apll>)
* The Axis operator to Ravel may transpose coordinates (e.g., <apll>,[2 1] R</apll> and <apll>,[1 2] R</apll> are both valid but, in general, have the same values in different order)
* The Axis operator is allowed on the dyadic derived function from the Each operator (e.g., <apll>(2 3⍴L)⍴¨[1 2] 2 3 4⍴R</apll>)
* The Axis operator is allowed on user-defined functions/operators (e.g., <apll>FOO[2 3] R</apll> by specifying it in the function header, as in <apll>∇ Z←FOO[X] R</apll>)
* If the first element of <apll>⎕FEATURE</apll> is a <apll>1</apll>, the Axis operator values may be negative. That is, if the largest allowed value is <apll>N</apll>, then the allowable range for axis operator values is <apll>1 ¯1[1]-N</apll> to <apll>N</apll>, inclusive.