Rewrite a good part of widont

site.py

         md = markdown_with_h2_anchors if with_h2_anchors else markdown_with_img_sizes
         for file_name in sorted(each_markdown_from(source)):
             result = md.read(source / file_name)
-            result = widont(result)
+            result = widont(result, html=True)
             # Extract (and remove) the title from the generated page.
             title, content = result.split("</h1>", 1)
             h1_opening_size = len("<h1>")

test_widont.py

+import pytest
+
+
+@pytest.mark.parametrize(
+    "in_,out_unicode, out_html",
+    [
+        ("", "", ""),
+        (" ", " ", " "),
+        ("A very simple test", "A very simple\u00a0test", "A very simple test"),
+        ("Test", "Test", "Test"),
+        (" Test", " Test", " Test"),
+        (
+            "<ul><li>Test</p></li><ul>",
+            "<ul><li>Test</p></li><ul>",
+            "<ul><li>Test</p></li><ul>",
+        ),
+        (
+            "<ul><li> Test</p></li><ul>",
+            "<ul><li> Test</p></li><ul>",
+            "<ul><li> Test</p></li><ul>",
+        ),
+        (
+            "<p>In a couple of paragraphs</p><p>paragraph two</p>",
+            "<p>In a couple of\u00a0paragraphs</p><p>paragraph\u00a0two</p>",
+            "<p>In a couple of&nbsp;paragraphs</p><p>paragraph&nbsp;two</p>",
+        ),
+        (
+            '<h1><a href="#">In a link inside a heading</i> </a></h1>',
+            '<h1><a href="#">In a link inside a\u00a0heading</i> </a></h1>',
+            '<h1><a href="#">In a link inside a&nbsp;heading</i> </a></h1>',
+        ),
+        (
+            '<h1><a href="#">In a link</a> followed by other text</h1>',
+            '<h1><a href="#">In a link</a> followed by other\u00a0text</h1>',
+            '<h1><a href="#">In a link</a> followed by other&nbsp;text</h1>',
+        ),
+        (
+            '<h1><a href="#"></a></h1>',
+            '<h1><a href="#"></a></h1>',
+            '<h1><a href="#"></a></h1>',
+        ),
+        (
+            "<div>Divs get no love!</div>",
+            "<div>Divs get no love!</div>",
+            "<div>Divs get no love!</div>",
+        ),
+        (
+            "<pre>Neither do PREs</pre>",
+            "<pre>Neither do PREs</pre>",
+            "<pre>Neither do PREs</pre>",
+        ),
+        (
+            "<div><p>But divs with paragraphs do!</p></div>",
+            "<div><p>But divs with paragraphs\u00a0do!</p></div>",
+            "<div><p>But divs with paragraphs&nbsp;do!</p></div>",
+        ),
+        (
+            "<p>Avec <mark>mon ami Marc.</mark></p>",
+            "<p>Avec <mark>mon ami\u00a0Marc.</mark></p>",
+            "<p>Avec <mark>mon ami&nbsp;Marc.</mark></p>",
+        ),
+        (
+            "Vraiment. Bien.",
+            "Vraiment. Bien.",
+            "Vraiment. Bien.",
+        ),
+    ],
+)
+def test_widont(in_, out_unicode, out_html):
+    from widont import widont
+
+    assert widont(in_) == out_unicode
+    assert widont(out_unicode) == out_unicode
+    assert widont(in_, html=True) == out_html
+    # TODO
+    # assert widont(out_html, html=True) == out_html

widont.py

 import re
+from dataclasses import dataclass
 
+import regex  # for the support of "\p{}"
 
-def widont(text):
-    """Replaces the space between the last two words in a string with `` ``
-    Works in these block tags ``(h1-h6, p, li, dd, dt)`` and also accounts for
-    potential closing inline elements ``a, em, strong, span, b, i, mark``
 
-    Extracted from:
+@dataclass
+class Charactere:
+    unicode: str
+    html: str
+
+
+NON_BREAKABLE_SPACE = Charactere(unicode="\u00a0", html=" ")
+
+# TODISCUSS: part of the configuration?
+COMPUTED_BLOCKS = "|".join(["p", "h[1-6]", "li", "dt", "dd"])
+ALLOWED_INLINES = "|".join(["a", "em", "span", "strong", "i", "b", "mark"])
+
+# \p{} allows to match a character by its Unicode category
+# "Zs" is the category "Separator, space".
+widont_finder = regex.compile(
+    rf"""(
+        # must be preceded by:
+        (?:</?                            # a closing tag
+            (?:{ALLOWED_INLINES})[^>]*>)  # an approved inline opening
+            |[^<>\s\.]                    # or a nontag/nonspace and not a point
+        )
+        \p{{Zs}}+                      # the space to replace
+        ([^<>\s]+                      # must be followed by non-tag non-space characters
+        \s*                            # optional white space!
+        (</({ALLOWED_INLINES})>\s*)*   # optional closing inline tags with optional white space after each
+        ((</({COMPUTED_BLOCKS})>)|$))  # end with a closing block or the end of the string
+    """,
+    re.VERBOSE,
+)
+
+
+def widont(text, html=False):
+    """Replaces the space between the last two words with non-breakable space
+
+    Works in block tags from COMPUTED_BLOCKS and also accounts for
+    potential closing inline elements in ALLOWED_INLINES.
+
+    Adapted from:
     https://github.com/mintchaos/typogrify/blob/
     20f693cbbb232ebc27733d9f1721a2cf1e7b25e3/typogrify/filters.py#L315-L368
 
-    >>> widont('A very simple test')
-    'A very simple&nbsp;test'
-    Single word items shouldn't be changed
-    >>> widont('Test')
-    'Test'
-    >>> widont(' Test')
-    ' Test'
-    >>> widont('<ul><li>Test</p></li><ul>')
-    '<ul><li>Test</p></li><ul>'
-    >>> widont('<ul><li> Test</p></li><ul>')
-    '<ul><li> Test</p></li><ul>'
-    >>> widont('<p>In a couple of paragraphs</p><p>paragraph two</p>')
-    '<p>In a couple of&nbsp;paragraphs</p><p>paragraph&nbsp;two</p>'
-    >>> widont('<h1><a href="#">In a link inside a heading</i> </a></h1>')
-    '<h1><a href="#">In a link inside a&nbsp;heading</i> </a></h1>'
-    >>> widont('<h1><a href="#">In a link</a> followed by other text</h1>')
-    '<h1><a href="#">In a link</a> followed by other&nbsp;text</h1>'
-    Empty HTMLs shouldn't error
-    >>> widont('<h1><a href="#"></a></h1>')
-    '<h1><a href="#"></a></h1>'
-    >>> widont('<div>Divs get no love!</div>')
-    '<div>Divs get no love!</div>'
-    >>> widont('<pre>Neither do PREs</pre>')
-    '<pre>Neither do PREs</pre>'
-    >>> widont('<div><p>But divs with paragraphs do!</p></div>')
-    '<div><p>But divs with paragraphs&nbsp;do!</p></div>'
-
-    Adaptations:
-    * add the mark element as a potential inline
-    * avoid insertion of a nbsp if the sentence is a single word
-
-    >>> widont("<p>Avec <mark>mon ami Marc.</mark></p>")
-    '<p>Avec <mark>mon ami&nbsp;Marc.</mark></p>'
-    >>> widont("Vraiment. Bien.")
-    'Vraiment. Bien.'
+    Improvements:
 
+    * allow the unbreakable unicode character (new option)
+    * add the mark element as a potential inline
+    * avoid insertion of a non-breakable space if the sentence is a single word
+    * externalized test suite
     """
-
-    widont_finder = re.compile(
-        r"""((?:</?(?:a|em|span|strong|i|b|mark)[^>]*>)|[^<>\s\.]) # must be preceded by an approved inline opening or closing tag or a nontag/nonspace
-            \s+                                                    # the space to replace
-            ([^<>\s]+                                              # must be followed by non-tag non-space characters
-            \s*                                                    # optional white space!
-            (</(a|em|span|strong|i|b|mark)>\s*)*                   # optional closing inline tags with optional white space after each
-            ((</(p|h[1-6]|li|dt|dd)>)|$))                          # end with a closing p, h1-6, li or the end of the string
-        """,
-        re.VERBOSE,
-    )
-    output = widont_finder.sub(r"\1&nbsp;\2", text)
+    spacer = NON_BREAKABLE_SPACE.html if html else NON_BREAKABLE_SPACE.unicode
+    output = widont_finder.sub(rf"\1{spacer}\2", text)
 
     return output