which elements are editable/writable/mutable?

[rodneyrehm]

The question is if we can safely identify "user alterable" elements, i.e. elements that accept keyboard input, e.g. <input>, [contenteditable], user-modify: read-write; as CSS Selectors Level 4's :read-write suggests.

This would allow us to provide is/mutable, which could power a new option filterMutable: true for ally.when.key to prevent key bindings for a to execute while the user is typing in an <input> element.