Detailed Specification
13. Graphics
[Disagreement with ANS]

13.2.5
  The remainder of the designated color index divided by 256 is used for the implemantation default.
13.3.5
  Even if the geometric object of a GRAPH LINES is fewer than two points, no exception shall be raised.
  In an array-cells statement, the remainder of the designated color index divided by 256 is used for the implemantation-defined default.
13.4.4
  Locate-statements and mat-locate-statements with a point-clause are available only on the BITMAP graphics mode. On execution of ASK PIXEL SIZE, the perimeter of the rectangle is assumed to be 'within' it.
13.5.4.2
  The beam shall be turned off before executing a MAT PLOT LINES statement.

[Implementation-defined]

13.1.4
  The Unit for device viewport and device size is meters.
13.1.6
  Inverted windows are valid.
13.3.6
  On execution of an array-cells statement, a zero-width or zero-height rectangular shall not be drawn.
13.3.6
  An exception with extype 6401 shall occur for a two-dimensional numeric-array in an array-point-list when the size of its second dimension is greater than 2.
13.5.4
  If a transformation is singular, an exception of extype -3009 shall be caused.

[Note]
Full BASIC may have ambiguous sentences.
Example.

    10 DEF ROTATE(x)=2*x
    20 DIM a(4,4)
    30 MAT a=IDN
    40 MAT a=ROTATE(PI/6)*a

The 20-line can be interpreted as both a numeric mat-statement and a transformation mat-statement. In these cases, THIS BASIC gives priority on the interpretation as a numeric mat-statement.