Breaking changes
[`ResolvedPos.marks`](https://prosemirror.net/docs/ref/version/0.23.0.html#model.ResolvedPos.marks) no longer takes a parameter (you probably want [`marksAcross`](https://prosemirror.net/doc/ref/version/0.23.0.html#model.ResolvedPos.marksAcross) if you were passing true there).
Attribute and mark constraints in [content expressions](https://prosemirror.net/docs/ref/version/0.23.0.html#model.NodeSpec.content) are no longer supported (this also means the `prosemirror-schema-table` package, which relied on them, is no longer supported). In this release, mark constraints are still (approximately) recognized with a warning, when present.
[`ContentMatch`](https://prosemirror.net/docs/ref/version/0.23.0.html#model.ContentMatch) objects lost a number of methods: `matchNode`, `matchToEnd`, `findWrappingFor` (which can be easily emulated using the remaining API), and `allowsMark`, which is now the responsibility of [node types](https://prosemirror.net/docs/ref/version/0.23.0.html#model.NodeType.allowsMarkType) instead.
[`ContentMatch.validEnd`](https://prosemirror.net/docs/ref/version/0.23.0.html#model.ContentMatch.validEnd) is now a property rather than a method.
[`ContentMatch.findWrapping`](https://prosemirror.net/docs/ref/version/0.23.0.html#model.ContentMatch.findWrapping) now returns an array of plain node types, with no attribute information (since this is no longer necessary).
The `compute` method for attributes is no longer supported.
Fragments no longer have an `offsetAt` method.
`DOMParser.schemaRules` is no longer public (use [`fromSchema`](https://prosemirror.net/docs/ref/version/0.23.0.html#model.DOMParser^fromSchema) and get the resulting parser's `rules` property instead).
The DOM parser option `topStart` has been replaced by [`topMatch`](https://prosemirror.net/docs/ref/version/0.23.0.html#model.ParseOptions.topMatch).
The `DOMSerializer` methods `nodesFromSchema` and `marksFromSchema` are no longer public (construct a serializer with [`fromSchema`](https://prosemirror.net/docs/ref/version/0.23.0.html#model.DOMSerializer^fromSchema) and read its `nodes` and `marks` properties instead).
Bug fixes
Fix issue where whitespace at node boundaries was sometimes dropped during content parsing.
Attribute default values of `undefined` are now allowed.
New features
[`contentElement`](https://prosemirror.net/docs/ref/version/0.23.0.html#model.ParseRule.contentElement) in parse rules may now be a function.
The new method [`ResolvedPos.marksAcross`](https://prosemirror.net/docs/ref/version/0.23.0.html#model.ResolvedPos.marksAcross) can be used to find the set of marks that should be preserved after a deletion.
[Content expressions](https://prosemirror.net/docs/ref/version/0.23.0.html#model.NodeSpec.content) are now a regular language, meaning all the operators can be nested and composed as desired, and a bunch of constraints on what could appear next to what have been lifted.
The starting content match for a node type now lives in [`NodeType.contentMatch`](https://prosemirror.net/docs/ref/version/0.23.0.html#model.NodeType.contentMatch).
Allowed marks are now specified per node, rather than in content expressions, using the [`marks`](https://prosemirror.net/docs/ref/version/0.23.0.html#model.NodeSpec.marks) property on the node spec.
Node types received new methods [`allowsMarkType`](https://prosemirror.net/docs/ref/version/0.23.0.html#model.NodeType.allowsMarkType), [`allowsMarks`](https://prosemirror.net/docs/ref/version/0.23.0.html#model.NodeType.allowsMarks), and [`allowedMarks`](https://prosemirror.net/docs/ref/version/0.23.0.html#model.NodeType.allowedMarks), which tell you about the marks that node supports.
The [`style`](https://prosemirror.net/docs/ref/version/0.23.0.html#model.ParseRule.style) property on parse rules may now have the form `"font-style=italic"` to only match styles that have the value after the equals sign.