Example uses a color that is not described in any way in documentation.

[ismagilli]

Version

3.1.9a

Details

Section 20.3 provides an example of a graph. To draw one of the lines, a color declared only in the documentation file:

pgf/doc/generic/pgf/pgfmanual-en-tikz-matrices.tex

Line 779 in 2131043

\draw [-,line width=8pt,draw=graphicbackground]

It seems to me that this example should be corrected.

---

I have two a suggestion to improve this example.

First based on using preaction:
replace

\draw [-,line width=8pt,draw=graphicbackground]
      (D) to [bend right, looseness=1] (A);
\draw (D) to [bend right, looseness=1]
      node [near start] {b} node [near end] {e} (A);

to

\draw [preaction={-,line width=8pt,draw=graphicbackground}]
      (D) to [bend right, looseness=1]
      node [near start] {b} node [near end] {e} (A);

Second based on this answer: replace

\begin{scope}[every node/.style={font=\small\itshape}]

to

\begin{scope}[every node/.style={font=\small\itshape},
              transparency group=knockout]

and replace draw=graphicbackground to draw,opacity=0. This will make the outline drawing independent of the background.

[ismagilli]

I found another example in the documentation where this color is used, but it clearly states that this is the background color:

pgf/doc/generic/pgf/pgfmanual-en-tikz-graphs.tex

Line 69 in 2131043

fill=graphicbackground}}, % yellowish background

[muzimuzhi]

I'm more in favor of adding similar comment to the first occurrence of graphicbackground.

Both examples use graphicbackground as the current background color, to manually implement some crossing/overlap effect. Not sure if an example for topic X should use advanced features in other topics or not. Using normal tricks may help newbies more focused on the current topic, while showing combinations of advanced features is a pursuit for perfection.

[Mo-Gul]

@a-is you are right, nowhere in the manual the definition of graphicbackground is given. But there are a lot of places in the manual where "information" is missing in examples. A few years ago even the needed libraries were missing. So that you get an impression, have a look at issue #640. I guess adding all needed information to all codeexamples would be an overkill. Therefore the idea was to have links to the individual codeexamples which then are fully defined and thus TeXable.

To support this you may have seen a few lines earlier to the quoted code line above that there is stated the definition of the color.

pgf/doc/generic/pgf/pgfmanual-en-tikz-matrices.tex

Line 761 in 2131043

pre={\definecolor{graphicbackground}{rgb}{0.96,0.96,0.8}},

I agree that we could add a comment here as in the other example. Feel free to provide a PR.

@muzimuzhi, regarding the code improvement: For me this is ok for the first example, because in that particular case these are ...

pgf/doc/generic/pgf/pgfmanual-en-tikz-matrices.tex

Lines 734 to 737 in 2131043

	\subsection{Examples}
	The following examples are adapted from code by Mark Wibrow. The first two
	redraw pictures from Timothy van Zandt's PStricks documentation: