Parse `==foo==` as `<mark>foo</mark>` in Mistune

Inspired by the syntax proposed by iaWriter.

site.py

@@ -30,7 +30,33 @@ NORMALIZED_STRFTIME = "%Y-%m-%dT12:00:00+01:00"
 TODAY = datetime.today() + timedelta(hours=6)
 
 
-class ImgsWithSizesRenderer(mistune.HTMLRenderer):
+class MarkParser(mistune.InlineParser):
+    """Parses `==foo==` as `<mark>foo</mark>`."""
+
+    MARK = (
+        r"(\={2})(?=[^\s*])("
+        r"(?:\\[\\*]|[^*])*"
+        r"(?:" + mistune.InlineParser.ESCAPE + r"|[^\s*]))\1"
+    )
+
+    RULE_NAMES = mistune.InlineParser.RULE_NAMES + ("mark",)
+
+    def parse_mark(self, m, state):
+        marker = m.group(1)
+        text = m.group(2)
+        return "mark", self.render(text, state)
+
+
+class MarkRenderer(mistune.HTMLRenderer):
+    """To use in conjunction with `MarkParser`."""
+
+    def mark(self, text):
+        return "<mark>" + text + "</mark>"
+
+
+class ImgsWithSizesRenderer(MarkRenderer):
+    """Renders images as <figure>s and add sizes (useful for lazy loading)."""
+
     def paragraph(self, text):
         # In case of a figure, we do not want the (non-standard) paragraph.
         if text.strip().startswith("<figure>"):
@@ -54,8 +80,9 @@ class ImgsWithSizesRenderer(mistune.HTMLRenderer):
 
 
 class H2AnchorsRenderer(ImgsWithSizesRenderer):
+    """Custom renderer for H2 titles with anchors."""
+
     def heading(self, text, level):
-        # Set an anchor to h2 headings.
         if level == 2:
             slug = slugify(text)
             return (
@@ -70,13 +97,17 @@ class H2AnchorsRenderer(ImgsWithSizesRenderer):
 
 
 # We want a custom renderer to create a hash/link for each H2 headings.
-markdown_with_h2_anchors = mistune.create_markdown(
-    renderer=H2AnchorsRenderer(escape=False), plugins=[DirectiveInclude()]
+markdown_with_h2_anchors = mistune.Markdown(
+    renderer=H2AnchorsRenderer(escape=False),
+    inline=MarkParser(H2AnchorsRenderer(escape=False)),
+    plugins=[DirectiveInclude()],
 )
 # The second markdown is pertinent to generate articles for the feed,
 # we do not need anchors in that case.
-markdown_with_img_sizes = mistune.create_markdown(
-    renderer=ImgsWithSizesRenderer(escape=False), plugins=[DirectiveInclude()]
+markdown_with_img_sizes = mistune.Markdown(
+    renderer=ImgsWithSizesRenderer(escape=False),
+    inline=MarkParser(ImgsWithSizesRenderer(escape=False)),
+    plugins=[DirectiveInclude()],
 )
 
 # This is the jinja2 configuration to locate templates.