Update th/td to use style attribute

This allows better interoperation with CSS style sheets, as the align
object on the TH is skipped if the css uses 'text-align: inherit' and
the previous 'text-align' is used instead (or the default: left).

Added an override to restore the original `align` behavior
Moved existing tests to the new test infrastructure
Added new tests to test the configuration parameter
Updated documentation to document the configuration parameter.

docs/change_log/index.md

@@ -3,6 +3,8 @@ title: Change Log
 Python-Markdown Change Log
 =========================
 
+Under development: version 3.4.0 ([Notes](release-3.4.md)).
+
 May 5, 2022: version 3.3.7 (a bug-fix release).
 
 * Disallow square brackets in reference link ids (#1209).

docs/change_log/release-3.4.md

@@ -0,0 +1,44 @@
+title: Release Notes for v3.4
+
+# Python-Markdown 3.4 Release Notes
+
+Python-Markdown version 3.4 supports Python versions 3.6, 3.7, 3.8, 3.9 and PyPy3.
+
+## Backwards-incompatible changes
+
+### The `table` extension now uses a `style` attribute instead of `align` attribute for alignment.
+
+The [HTML4 spec][spec4] specifically
+deprecates the use of the `align` attribute and it does not appear at all in the 
+[HTML5 spec][spec5]. Therefore, by default, the [table] extension will now use the `style`
+attribute (setting just the `text-align` property) in `td` and `th` blocks.
+
+[spec4]: https://www.w3.org/TR/html4/present/graphics.html#h-15.1.2
+[spec5]: https://www.w3.org/TR/html53/tabular-data.html#attributes-common-to-td-and-th-elements
+
+The former behavior is available by setting the setting `use_align_attribute` configuration
+option to `True` when adding the extension.
+
+For example, to configure the old `align` behavior:
+
+```python
+from markdown.extensions.tables import TableExtension
+
+markdown.markdown(src, extensions=[TableExtension(use_align_attribute=True)])
+```
+
+In addition, tests were moved to the modern test environment.
+
+## New features
+
+The following new features have been included in the 3.3 release:
+
+* Use `style` attribute in tables for alignment instead of `align` for better CSS
+  inter-operation. The old behavior is available by setting `use_align_attribute=True` when
+  adding the extension.
+
+## Bug fixes
+
+The following bug fixes are included in the 3.4 release:
+
+

docs/extensions/tables.md

@@ -58,10 +58,30 @@ Usage
 See [Extensions](index.md) for general extension usage. Use `tables` as the
 name of the extension.
 
-This extension does not accept any special configuration options.
+See the [Library Reference](../reference.md#extensions) for information about
+configuring extensions.
+
+The following options are provided to change the default behavior:
+
+* **`use_align_attribute`**: Set to `True` to use `align` instead of an appropriate `style` attribute
+
+    Default: `'False'`
+
 
 A trivial example:
 
 ```python
 markdown.markdown(some_text, extensions=['tables'])
 ```
+
+### Examples
+
+For an example, let us suppose that alignment should be controlled by the legacy `align`
+attribute.
+
+```pycon
+>>> from markdown.extensions.tables import TableExtension
+>>> html = markdown.markdown(text,
+...                 extensions=[TableExtension(use_align_attribute=True)]
+... )
+```

markdown/extensions/tables.py

@@ -30,9 +30,11 @@ class TableProcessor(BlockProcessor):
     RE_CODE_PIPES = re.compile(r'(?:(\\\\)|(\\`+)|(`+)|(\\\|)|(\|))')
     RE_END_BORDER = re.compile(r'(?<!\\)(?:\\\\)*\|$')
 
-    def __init__(self, parser):
+    def __init__(self, parser, config):
         self.border = False
         self.separator = ''
+        self.config = config
+
         super().__init__(parser)
 
     def test(self, parent, block):
@@ -126,7 +128,10 @@ def _build_row(self, row, parent, align):
             except IndexError:  # pragma: no cover
                 c.text = ""
             if a:
-                c.set('align', a)
+                if self.config['use_align_attribute']:
+                    c.set('align', a)
+                else:
+                    c.set('style', f'text-align: {a};')
 
     def _split_row(self, row):
         """ split a row of text into list of cells. """
@@ -212,11 +217,19 @@ def _split(self, row):
 class TableExtension(Extension):
     """ Add tables to Markdown. """
 
+    def __init__(self, **kwargs):
+        self.config = {
+            'use_align_attribute': [False, 'True to use align attribute instead of style.'],
+        }
+
+        super().__init__(**kwargs)
+
     def extendMarkdown(self, md):
         """ Add an instance of TableProcessor to BlockParser. """
         if '|' not in md.ESCAPED_CHARS:
             md.ESCAPED_CHARS.append('|')
-        md.parser.blockprocessors.register(TableProcessor(md.parser), 'table', 75)
+        processor = TableProcessor(md.parser, self.getConfigs())
+        md.parser.blockprocessors.register(processor, 'table', 75)
 
 
 def makeExtension(**kwargs):  # pragma: no cover