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3 . PENDRAW LANGUAGE GRAPHICS
3.1 PRINCIPLES

These are the basics of PenDraw

Everything you do with PenDraw comes down to moving a notional 'pen': from one point to another: from one Pen State to another.
PenDraw deals in Pics, which can draw and/or carry out calculations.
Pics draw either through the Draw instruction (which involves other Pics) or the PEN instruction, which can produce

In PenDraw you are DRAWing Pics on a sheet of paper, or on a screen. You may Draw Pics from within other Pics.
When you DRAW a Pic you may give it attributes, such as position, scale and orientation.
You can stop an attribute affecting a Pic by making the Pic special. Take rotation of a Pic, for example. Apply the Specialty that prevents rotation. Default Turn prevents rotation, and PenDraw will not rotate that Pic with respect to its DRAWING's axes.
This is the difference between a Pic and a DRAWING: a DRAWING is the frame of reference for Specialty Default whereas a Pic is not. Although you may prevent rotation (for example) of a Pic, and the Pic will then not rotate with respect to its DRAWING, the DRAWING could be rotated and the Pic would rotate with it.
That is all there is to the principles, or framework, of PenDraw. The rest is detail (plenty of it: PenDraw has a very rich set of graphics capabilities): what all the possible attributes are, what the possible Specialties are, how to pass parameters to PenDraw and so forth. The framework is clear and simple: built to be the base on which the details combine and work in predictable, consistent ways. The strength of using PenDraw lies in identifying the details you need and combining them intelligently.

To sum up more succinctly, the basics of PenDraw are

and a few other Pics we have pre-defined to make life simpler, plus other Pics, that YOU define for yourself.