Handle subsets of syntax not supported by analysis in a user-friendly way.

[lapets]

• Use carousels as on this line to ensure that for any node types not handled by the analysis, an error is returned.
• If possible, convert the above to instead somehow mark (using a new attribute of each node, for example) which parts of the subtree are not handled. Then, in some way highlight those parts of the subtree in the input text editor so they can see what part of their program is using unsupported syntax.
• If the above is too difficult, then display a mirror copy of the original source code and highlight the unsupported regions of the syntax there. This can be a new tab.