in Maple 11 and 12

In Classic GUI (Maple 12) the above export command produces a plot of 215x215pt (after Ghostscript) without left/bottom margin. But in Standard GUI (Maple 11 and 12) I get a box within corners  20,119pt  and 573,672pt. That is, independently of the height and width parameters in the 'plotsetup' statement and with left/bottom margins of 20pt.

So, use the Classic GUI.

in Maple 11 and 12

In Classic GUI (Maple 12) the above export command produces a plot of 215x215pt (after Ghostscript) without left/bottom margin. But in Standard GUI (Maple 11 and 12) I get a box within corners  20,119pt  and 573,672pt. That is, independently of the height and width parameters in the 'plotsetup' statement and with left/bottom margins of 20pt.

So, use the Classic GUI.

I think that here it is meant PDE in the sense of distributions.

In fact, in Maple this is the "normal" role of 'Heaviside':

?Heaviside

 The Heaviside function is also the anti-derivative of Dirac in that...

I think that here it is meant PDE in the sense of distributions.

In fact, in Maple this is the "normal" role of 'Heaviside':

?Heaviside

 The Heaviside function is also the anti-derivative of Dirac in that...

right now. The Standard GUI has many options to hide/show things. May be that your setting is different to mine. Look at Tools > Options > Display. Eg. I have "Display output from Evaluate (Document Blocks)" checked.

Hidding. Some statements available about its purpose.
Eg here:

An important decision when creating any technical document, presentation, or application is the amount of technical detail. With Maple 10, your important points are not hidden amongst derivations, commands, and extra white space. You can hide intermediate computations, show results in the middle of a block of text, and not enter or show a single Maple command.

And here

The second method is to display the result, following the input expression and to display, between the two, a short text or symbol (e.g., an arrow) that describes the operation that was applied. This makes the document visually appealing and close to what one would expect to see in a mathematical textbook. There is no textual command or syntax that may be a distraction from the actual content that the document is supposed to convey. The disadvantage of this method is that, although the exact semantics of the operation can be preserved behind the scenes, in order to automatically update results if the input changes, the semantics of the operation are not obvious to a reader of the document. Because the presentation has to be visually appealing, the description of the operation has to be more casual or imprecise.

I think that in practice, things are more complicated and confusion may arise. So, I find that it is much easier to learn Maple using worksheets.

This is what I get in Maple 11.02:

with(share);
See ?share and ?share,contents for information about the share library
                                  []
with(TDTools);
Share Library: TDTools
Authors: Taylor, Ross
Description: Tools for manipulating derivatives and differentials

  ["Compare_Eqn", "D2Diff", "D2I", "DiffFlip", "Flipeqn", "TD",
   "TDiff", "TInt", "Tdiff", "Tint", "solveqn"]

As said before, 'TDiff' works except for sums, as far as I have tested it.

This is what I get in Maple 11.02:

with(share);
See ?share and ?share,contents for information about the share library
                                  []
with(TDTools);
Share Library: TDTools
Authors: Taylor, Ross
Description: Tools for manipulating derivatives and differentials

  ["Compare_Eqn", "D2Diff", "D2I", "DiffFlip", "Flipeqn", "TD",
   "TDiff", "TInt", "Tdiff", "Tint", "solveqn"]

As said before, 'TDiff' works except for sums, as far as I have tested it.

and RREF works: View 143_rref.mw on MapleNet or Download 143_rref.mw
View file details

From my point of view, this document mode is a source of confusion, as its purpose is to hide "details". If I were you, I would use worksheets and 1D input.

Installing this version of the share library in Maple 11.02, I see that 'TDiff' from the package 'TDTools' does work as expected for the cases of the example worksheet ?share,TDTools,TDTools_mws but not as shown in that article, for the case of  differentiation under a sum.

Have you been able to reproduce that result, or make it work for the problem stated here?

'chemeng' is a "package" of example worksheets.

Installing this version of the share library in Maple 11.02, I see that 'TDiff' from the package 'TDTools' does work as expected for the cases of the example worksheet ?share,TDTools,TDTools_mws but not as shown in that article, for the case of  differentiation under a sum.

Have you been able to reproduce that result, or make it work for the problem stated here?

'chemeng' is a "package" of example worksheets.

The analysis that I have made in this blog of the available evidence seems to show that a Maplesoft supported wiki is unlikely.

You may also try in Maple 12:

with(MTM):
M := Matrix(2,3,'fill'=x*y):
diff(M,x);

                                          [y    y    y]
                                          [           ]
                                          [y    y    y]

You may also try in Maple 12:

with(MTM):
M := Matrix(2,3,'fill'=x*y):
diff(M,x);

                                          [y    y    y]
                                          [           ]
                                          [y    y    y]

But recently there was some confusion about the Maple Reader (player).

Where precisely are these statements?