* rename state to value in slate core, as deprecation
* rename all references to state to value in slate core
* migrate slate-base64-serializer
* migrate slate-html-serializer
* migrate slate-hyperscript
* migrate slate-plain-serializer
* migrate slate-prop-types
* migrate slate-simulator
* fix change.setState compat
* deprecate references to state in slate-react
* remove all references to state in slate-react
* remove `value` and `schema` from props to all components
* fix default renderPlaceholder
* fix tests
* update examples
* update walkthroughs
* update guides
* update reference
* remove data from event handler signatures
* standardize known transfer types
* add setEventTransfer to docs
* update examples, fix drag/drop
* fix tests and draggable attribute setting
* refactor to extract applyOperation util
* change handlers to receive transform instead of state
* change onChange to receive a transform, update rich-text example
* fix stack iterationg, convert check-list example
* convert code-highlighting, embeds, emojis examples
* change operations to use full paths, not indexes
* switch split and join to be recursive
* fix linter
* fix onChange calls
* make all operations invertable, add src/operations/* logic
* rename "join" to "merge"
* remove .length property of nodes
* fix node.getFragmentAtRange logic
* convert remaining examples, fix existing changes
* fix .apply() calls and tests
* change setSave and setIsNative transforms
* fix insert_text operations to include marks always
* cleanup and fixes
* fix node inheritance
* fix core onCut handler
* skip constructor in node inheritance
* cleanup
* change updateDescendant to updateNode
* add and update docs
* eliminate need for .apply(), change history to mutable
* add missing file
* add deprecation support to Transform objects
* rename "transform" to "change"
* update benchmark
* add deprecation util to logger
* update transform isNative attr
* fix remaining warn use
* simplify history checkpointing logic
* fix tests
* revert history to being immutable
* fix history
* fix normalize
* fix syntax error from merge
* WIP getting raw marks arrays from the current range
* Always handle marksRaw as Array, fixes tests/lint
* Clean up
* Fixes collapsed selection raw marks, simpler _every_ condition, harmonize toolbar buttons in rich-text example
* raw -> perCharacter
* Add tests for toggleMark collapsed selection
* Add .DS_Store to .gitignore
* Added test for toggleMark add in partially marked selection, with and without other marks
* Added docs for state.marksPerCharacter
* replace marksPerCharacter with activeMarks
* Update the other examples
* Clarify getActiveMarksAtRange
* AddMark/RemoveMark to use getActiveMarksByRange
* User activeMarks for toggle§MarkAtRange transform
* putting in the correct type pseudo-symbols
* getting the pseudo symbols everywhere that the instance of's are
* Making Ian's suggestions on checking types with static methods
* cleaning up leftover hard checks
* adding in slate proptypes, cleaning up unneeded whitespace
* updating documentation, moving keys to prototypes finally, al tests passing
* organizing types, prop-types, more succint type names
* eslint fix
* fixing model-types bug, changing proptype names
* Replace cheerio with parse5
* Convert to dependency injection for HTML parser
* Add options.domParser to HTML serializer
* Fallback to native DOMParser if present and no option provided
* Error if no DOM parser is available (option or native)
* Update tests to pass parse5 as config option
* Update test so it passes.
Cheerio interprets `<p><hr /></p>` as one `p` node with a child `hr`
node, but both parse5 and native DOMParser interpret it as 3 nodes: a
blank `p` node, `hr` node, and second blank `p` node. Update test
expectation to match new API.
* Remove cheerio-esque compatibility conversion.
* Use `application/xml` in native DOMParser
Using `text/html` causes it to wrap the fragment in html, body, etc
* Change error message to single line.
Was inserting an undesired newline char
* Add documentation for new `domParser` option to html serializer
Also boyscout missing documentation for `defaultBlockType` option
* Rename `domParser` option to `parseHtml`
Rename the option to make it clearer what it does, since it accepts a
function and not a `DOMParser` analogue object.
* Add property isEmpty to State
* Update hovering menu example
* Document isEmpty
* Improve perf of isEmpty with @Soreine 's suggestion
* Fix return of isEmpty
I tried using the exact code from the example to be met by errors.
The order of arguments in the function example is wrong, it should be use the API described in the [docs](https://docs.slatejs.org/reference/plugins/plugin.html#onbeforeinput).
```
Function onBeforeInput(event: Event, data: Object, state: State, editor: Editor) => State || Void
```
* Adding firstOnly prop to Placeholder
Partly addresses #737
* Updating placeholder logic to check for parent only if firstOnly is set to true
* removing extra newlines
* simplifying shouldComponentUpdate condition
