Impact and strategy for polyfills

In the various discussions on deprecating and simplifying the various features, elements and attributes of MathML, as well as whether or not a given feature should be present in MathML Core, one of the key factors in the decision is whether the feature in question can be recovered by use of a polyfill. I would like to start a discussion about how the group envisions polyfills being used.

For purpose of argument, let us assume that every feature in in the main spec but missing from Core would/could be implemented by a polyfill. We would need appropriate Feature Detection for each feature as well, which seems in some cases harder than the polyfill itself(?)

• Is including polyfills an author or browser responsibility?
• Would there be a standard set of feature/polyfill pairs?
• A master polyfill?
• A method to determine which polyfills are needed?
• General questions about performance trade-offs (both rendering and network).
  Presumably more questions will arise as we discuss :>

Start by reviewing the issue's questions alongside the MathML Core and deprecation discussions it references. A useful outcome would be a documented group position on author versus browser responsibility, feature detection, standard polyfill sets, and performance trade-offs; no specific files or tests are identified.