Technical details for the TSDoc syntax are tracked by "RFC" issues with the Request for Comments GitHub label.
The @microsoft/tsdoc package provides a feature complete reference implementation of a parser, and many syntax details are explained in the code comments for its source code.
This section is still under development. We'll post more detail soon.
The "old" syntax for declaration references is detailed in this technical note:
The "new" syntax for declaration references is described in this grammar:
Examples of the new syntax can be found in the DeclarationReference.test.ts file.