When I tested the page in Firefox's Reader View, I got an empty grid, and when I tested it in Firefox's Print Preview, I just got the coordinates around the sides without the grid lines. Ideally, the diagram should always display the board.
This is really strange. (But it also happens for me.) Because the coordinates are something that is generated at load time, just as the rest of the diagram. I could have understood it when it would have printed no diagram at all, or just the definition of the Diagram. That would mean that it is printing the page as it looks in Page Source. But it must have been running the JavaScript to get those coordinates. But not completely, or you would have seen the rest of the Diagram. Perhaps the JavaScript chokes during display of the position, because some HTML elements it tries to refer to are no longer present on the Print Preview page.
This is actually a bad problem, as it means that all pages I put Interactive Diagrams in have become unprintable. (In FireFox. I don't know if other browsers behave the same.)
One solution would be to provide a link/button on each such page to switch it to a special printable version. E.g. as if JavaScript has been switched off, using the static image of the setup. This could be done by not putting that image in noscript tags, but in a DIV section, which would be hidden by the JavaScript at the same time as it creates the Interactive Diagram and makes that visible. And have the 'Printable Version' link reverse that.
[Edit] I noticed that the message you currently print at the top of each page ("The site has moved...") in the Print Preview is printed with black text on a white background, while on the page it was on a black field. So it seems that the Print Preview is stripping style attributes and enforcing its own style to HTML elements. That explains the disappearance of the table borders and board checkering. It also explains the disappearance of the pieces: the Diagram renders these as background to the table cells (so that the highlighting markers can be displayed on top of them as cell content). Background images are also a style. Indeed, when I select a piece in the Diagram to get its moves highlighted, and then ask for the Print Preview, the highlighting markers are visible in the Preview.
[Edit2] Chrome behaves similarly, except that it does keep table borders (so that grid lines remain visible in the Diagram).
This is really strange. (But it also happens for me.) Because the coordinates are something that is generated at load time, just as the rest of the diagram. I could have understood it when it would have printed no diagram at all, or just the definition of the Diagram. That would mean that it is printing the page as it looks in Page Source. But it must have been running the JavaScript to get those coordinates. But not completely, or you would have seen the rest of the Diagram. Perhaps the JavaScript chokes during display of the position, because some HTML elements it tries to refer to are no longer present on the Print Preview page.
This is actually a bad problem, as it means that all pages I put Interactive Diagrams in have become unprintable. (In FireFox. I don't know if other browsers behave the same.)
One solution would be to provide a link/button on each such page to switch it to a special printable version. E.g. as if JavaScript has been switched off, using the static image of the setup. This could be done by not putting that image in noscript tags, but in a DIV section, which would be hidden by the JavaScript at the same time as it creates the Interactive Diagram and makes that visible. And have the 'Printable Version' link reverse that.
[Edit] I noticed that the message you currently print at the top of each page ("The site has moved...") in the Print Preview is printed with black text on a white background, while on the page it was on a black field. So it seems that the Print Preview is stripping style attributes and enforcing its own style to HTML elements. That explains the disappearance of the table borders and board checkering. It also explains the disappearance of the pieces: the Diagram renders these as background to the table cells (so that the highlighting markers can be displayed on top of them as cell content). Background images are also a style. Indeed, when I select a piece in the Diagram to get its moves highlighted, and then ask for the Print Preview, the highlighting markers are visible in the Preview.
[Edit2] Chrome behaves similarly, except that it does keep table borders (so that grid lines remain visible in the Diagram).