Dash

- New `icicle` trace type.
- New `legendrank` trace attribute.
- Several other additions and bug fixes.

- Stop exporting d3 as `Plotly.d3`, and remove many other deep pieces of the public API. This does not affect the `dcc.Graph` component, but if you make use of `Plotly` from the global scope in some other way you may be affected.
- Drop the deprecated trace types `contourgl` and `area`, as well as legacy pre-`scatterpolar` polar attributes `bar.r`, `bar.t`, `scatter.r`, `scatter.t`, `layout.radialaxis`, `layout.angularaxis`. Use `scatterpolar`, `barpolar`, and `polar` subplots instead.
- `heatmapgl` and `pointcloud` trace types, and the `transform` attribute are deprecated, and will be removed in a future release.
- Increase CSP safety by removing function constructors. 3D plots still use function constructors, but if you place one of the non-3D bundles (including the new `strict` bundle) in your `assets` folder you will have no function constructors.
- Remove "Aa" text in legends.
- Default `hovermode` to "closest".
- Default `textposition` to "auto" in `bar` traces. If you previously used the `bar.text` attribute for hover only, you will need to explicitly set `textposition="none"`.
- Add `bar.marker.pattern`, `image.zsmooth`, and various other features and bugfixes.

Added
- [888](https://github.com/plotly/dash-core-components/pull/888) Adds a `drag_value` prop to `dcc.Slider`to be able to fire callbacks from dragging and releasing the slider.

Dash HTML Components
Fixed
- [169](https://github.com/plotly/dash-html-components/pull/169) - part of fixing dash import bug https://github.com/plotly/dash/issues/1143

Dash Table
Fixed
- [854](https://github.com/plotly/dash-table/pull/854) - part of fixing dash import bug https://github.com/plotly/dash/issues/1143

Dash and Dash Renderer
Added
- [1675](https://github.com/plotly/dash/pull/1675) Add new `Dash` constructor argument `extra_hot_reload_paths`. This allows you to re-initialize the Python code of the app when non-Python files change, if you know that these files impact the app.

Changed
- [1675](https://github.com/plotly/dash/pull/1675) Remove the constraint that `requests_pathname_prefix` ends with `routes_pathname_prefix`. When you are serving your app behind a reverse proxy that rewrites URLs that constraint needs to be violated.
- [1611](https://github.com/plotly/dash/pull/1611) and [#1685](https://github.com/plotly/dash/pull/1685) Package dash-renderer artifacts and dependencies with Dash, and source renderer resources from within Dash.
- [1567](https://github.com/plotly/dash/pull/1567) Julia component generator puts components into `src/jl` - fixes an issue on case-insensitive filesystems when the component name and module name match (modulo case) and no prefix is used. Also reduces JS/Julia clutter in the overloaded `src` directory.

Fixed
- [1664](https://github.com/plotly/dash/pull/1664) Fix [#1649](https://github.com/plotly/dash/issues/1649), makes the devtools readable with a dark theme.
- [1640](https://github.com/plotly/dash/pull/1640) Fix [#1475](https://github.com/plotly/dash/issues/1475), missing `timing_information` after certain modifications to Flask behavior

Dash Core Components
Fixed

- [963](https://github.com/plotly/dash-core-components/pull/963) Fixes [#885](https://github.com/plotly/dash-core-components/issues/885)

This applies the fix from [878](https://github.com/plotly/dash-core-components/pull/878) to the RangeSlider.
It not only fixes the bug where the tooltips were visible when slider was not, but it also reduces the lag in the
tooltip when the slider handles are moved.

Updated
- [939](https://github.com/plotly/dash-core-components/pull/939) Upgrade Plotly.js to v2.2.1. Note that this is a major version upgrade to Plotly.js, however we are not treating this as a breaking change for DCC as the majority of breaking changes in Plotly.js do not affect the Dash API. The one exception is that several trace types that have long been deprecated are removed entirely.

Dash and Dash Renderer
Changed
- [1531](https://github.com/plotly/dash/pull/1531) Update the format of the docstrings to make them easier to read in the reference pages of Dash Docs and in the console. This also addresses [#1205](https://github.com/plotly/dash/issues/1205)
- [1553](https://github.com/plotly/dash/pull/1553) Increase the z-index of the Dash error menu from 1001 to 1100 in order to make sure it appears above Bootstrap components.

Fixed
- [1546](https://github.com/plotly/dash/pull/1546) Validate callback request `outputs` vs `output` to avoid a perceived security issue.

Dash Core Components
Added
- [863](https://github.com/plotly/dash-core-components/pull/863) Adds a new `Download` component. Along with this several utility functions are added to help construct the appropriate data format:
- `dcc.send_file` - send a file from disk
- `dcc.send_data_frame` - send a `DataFrame`, using one of its writer methods
- `dcc.send_bytes` - send a bytestring or the result of a bytestring writer
- `dcc.send_string` - send a string or the result of a string writer

Changed
- [923](https://github.com/plotly/dash-core-components/pull/923)
Set `autoComplete` to off in `dcc.Dropdown`. This fixes [808](https://github.com/plotly/dash-core-components/issues/808)

Fixed
- [930](https://github.com/plotly/dash-core-components/pull/930) Fixed a bug [#867](https://github.com/plotly/dash-core-components/issues/867) with `DatePickerRange` that would sometimes shift the allowed dates by one day.
- [934](https://github.com/plotly/dash-core-components/pull/934) Fixed a bug in `EnhancedTab` component that ignored `disabled_className` property

Dash HTML Components
Fixed
- [179](https://github.com/plotly/dash-html-components/pull/179) - Fixes [#77](https://github.com/plotly/dash-html-components/issues/77) Added `allow` and `referrerPolicy` properties to `html.Iframe`

- [178](https://github.com/plotly/dash-html-components/pull/178) - Fix [#161](https://github.com/plotly/dash-html-components/issues/161) <object> `data` property, and fix [#129](https://github.com/plotly/dash-html-components/issues/129) obsolete, deprecated, and discouraged elements. No elements were removed, but comments were added to the documentation about these elements detailing their limitations.

Dash Table
Changed
- [862](https://github.com/plotly/dash-table/pull/862) - update docstrings per https://github.com/plotly/dash/issues/1205
- [878](https://github.com/plotly/dash-table/pull/878) - update build process to use Webpack 5 and other latest dependencies