Markdown

Fixed

* Add `checklinks` tox environment to ensure all links in documentation are good.
* Refactor extension API documentation (729).
* Load entry_points (for extensions) only once using `importlib.metadata`.
* Do not double escape entities in TOC.
* Correctly report if an extension raises a `TypeError` (939).
* Raise a `KeyError` when attempting to delete a nonexistent key from the
extension registry (939).
* Remove import of `packaging` (or `pkg_resources` fallback) entirely.
* Remove `setuptools` as a run-time dependency (`install_required`).

Fixed

* The `name` property in `toc_tokens` from the TOC extension now
escapes HTML special characters (`<`, `>`, and `&`).

Changed

Drop support for Python 2.7

Python 2.7 reaches end-of-life on 2020-01-01 and Python-Markdown 3.2 has dropped
support for it. Please upgrade to Python 3, or use Python-Markdown 3.1.

`em` and `strong` inline processor changes

In order to fix issue 792, `em`/`strong` inline processors were refactored. This
translated into removing many of the existing inline processors that handled this
logic:

* `em_strong`
* `strong`
* `emphasis`
* `strong2`
* `emphasis`

These processors were replaced with two new ones:

* `em_strong`
* `em_strong2`

The [`legacy_em`](extensions/legacy_em.md) extension was also modified with new,
refactored logic and simply overrides the `em_strong2` inline processor.

CodeHilite now always wraps with `<code>` tags

Before, the HTML generated by CodeHilite looked like:
- `<pre><code>foo = 'bar'</code></pre>` if you **were not** using Pygments.
- `<pre>foo = 'bar'</pre>` if you **were** using Pygments.

To make the cases more consistent (and adhere to many Markdown specifications and
HTML code block markup suggestions), CodeHilite will now always additionally wrap
code with `<code>` tags. See 862 for more details.

This change does not alter the Python-Markdown API, but users relying on the old
markup will find their output now changed.

Internally, this change relies on the Pygments 2.4, so you must be using at least
that version to see this effect. Users with earlier Pygments versions will
continue to see the old behavior.

`markdown.util.etree` deprecated

Previously, Python-Markdown was using either the `xml.etree.cElementTree` module
or the `xml.etree.ElementTree` module, based on their availability. In modern
Python versions, the former is a deprecated alias for the latter. Thus, the
compatibility layer is deprecated and extensions are advised to use
`xml.etree.ElementTree` directly. Importing `markdown.util.etree` will raise
a `DeprecationWarning` beginning in version 3.2 and may be removed in a future
release.

Therefore, extension developers are encouraged to replace
`from markdown.util import etree` with
`import xml.etree.ElementTree as etree` in their code.

Added

* Some new configuration options have been added to the [toc](extensions/toc.md)
extension:

* The `anchorlink_class` and `permalink_class` options allow class(es) to be
assigned to the `anchorlink` and `permalink` respectively. This allows using
icon fonts from CSS for the links. Therefore, an empty string passed to
`permalink` now generates an empty `permalink`. Previously no `permalink`
would have been generated. (776)

* The `permalink_title` option allows the title attribute of a `permalink` to be
set to something other than the default English string `Permanent link`. (877)

* Document thread safety (812).

* Markdown parsing in HTML has been exposed via a separate extension called
[`md_in_html`](extensions/md_in_html.md).

* Add support for Python 3.8.

Fixed

* HTML tag placeholders are no longer included in `.toc_tokens` (899).
* Unescape backslash-escaped characters in TOC ids (864).
* Refactor bold and italic logic in order to solve complex nesting issues (792).
* Always wrap CodeHilite code in `code` tags (862).

Fixed

* Fixed import failure in `setup.py` when the source directory is not
on `sys.path` (823).
* Prefer public `packaging` module to pkg_resources' private copy of
it (825).

the legacy attributes will raise a `DeprecationWarning` if they are accessed. In
a future release the legacy attributes will be removed.

Added

* A [Contributing Guide](contributing.md) has been added (732).

* A new configuration option to set the footnote separator has been added. Also,
the `rel` and `rev` attributes have been removed from footnotes as they are
not valid in HTML5. The `refs` and `backrefs` classes already exist and
serve the same purpose (723).

* A new option for `toc_depth` to set not only the bottom section level,
but also the top section level. A string consisting of two digits
separated by a hyphen in between (`"2-5"`), defines the top (`t`) and the
bottom (`b`) (`<ht>..<hb>`). A single integer still defines the bottom
section level (`<h1>..<hb>`) only. (787).

Fixed

* Update CLI to support PyYAML 5.1.
* Overlapping raw HTML matches no longer leave placeholders behind (458).
* Emphasis patterns now recognize newline characters as whitespace (783).
* Version format had been updated to be PEP 440 compliant (736).
* Block level elements are defined per instance, not as class attributes
(731).
* Double escaping of block code has been eliminated (725).
* Problems with newlines in references has been fixed (742).
* Escaped `` are now handled in header syntax (762).

Fixed

* Brought back the `version` and `version_info` variables (709).
* Added support for hexadecimal HTML entities (712).