⎕PW is the maximum number of output characters per line before folding the display.
⎕PW may be assigned any integer value in the range 42 to 32767. Note that in versions of Dyalog APL prior to 13.0 ⎕PW had a minimum value of 30; this was increased to support 128-bit decimal values.
If an attempt is made to display a line wider than ⎕PW, then the display will be folded at or before the ⎕PW width and the folded portions indented 6 spaces. The display of a simple numeric array may be folded at a width less than ⎕PW so that individual numbers are not split.
⎕PW only affects output, either direct or through ⎕ output. It does not affect the result of the function Format (⍕), of the system function ⎕FMT, or output through the system functions ⎕ARBOUT and ⎕ARBIN, or output through ⍞.
Note that if the auto_pw parameter (Options/Configure/Session/Auto PW) is set to 1, ⎕PW is automatically adjusted whenever the Session window is resized. In these circumstances, a value assigned to ⎕PW will only apply until the Session window is next resized.
⎕PW←42 ⎕←3⍴÷3 0.3333333333 0.3333333333 0.3333333333 0.3333333333