Add a title attribute to rendered iframes for accessibility

Accessibility audits flag the iframe that branca renders in notebooks with
"frames must have an accessible name" (WCAG 2.1), because the iframe has no
title attribute (#213).

Emit a title attribute when one is available:

- Figure reuses its existing title, so Figure(title="...") now names both
  the document <title> and the iframe.
- IFrame gains a title parameter.

When no title is set the output is byte-for-byte unchanged, so existing
maps are unaffected; the title is HTML-escaped so a value containing a
quote cannot break out of the attribute.

Builds on #235 (both touch the same iframe templates); the net new change
here is the title attribute.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: Htet-Kaung-San

branca/element.py

@@ -328,7 +328,8 @@ class Figure(Element):
         A percentage defining the aspect ratio of the Figure.
         It will be ignored if height is not None.
     title : str, default None
-        Figure title.
+        Figure title. Also used as the ``title`` attribute (accessible
+        name) of the iframe when the Figure is displayed in a notebook.
     figsize : tuple of two int, default None
         If you're a matplotlib addict, you can overwrite width and
         height. Values will be converted into pixels in using 60 dpi.
@@ -412,24 +413,31 @@ def render(self, **kwargs) -> str:
     def _repr_html_(self, **kwargs) -> str:
         """Displays the Figure in a Jupyter notebook."""
         html = escape(self.render(**kwargs))
+        # Give the iframe an accessible name when a title is set, so it is
+        # not flagged by "frames must have an accessible name" audits.
+        title_attr = f' title="{escape(self.title)}"' if self.title else ""
         if self.height is None:
             iframe = (
                 '<div style="width:{width};">'
                 '<div style="position:relative;width:100%;height:0;padding-bottom:{ratio};">'  # noqa
                 '<span style="color:#565656">Make this Notebook Trusted to load map: File -> Trust Notebook</span>'  # noqa
-                '<iframe srcdoc="{html}" style="position:absolute;width:100%;height:100%;left:0;top:0;'  # noqa
+                '<iframe srcdoc="{html}"{title_attr} style="position:absolute;width:100%;height:100%;left:0;top:0;'  # noqa
                 'border:none !important;" '
                 "allowfullscreen webkitallowfullscreen mozallowfullscreen>"
                 "</iframe>"
                 "</div></div>"
-            ).format(html=html, width=self.width, ratio=self.ratio)
+            ).format(
+                html=html, width=self.width, ratio=self.ratio, title_attr=title_attr
+            )
         else:
             iframe = (
-                '<iframe srcdoc="{html}" width="{width}" height="{height}" '
+                '<iframe srcdoc="{html}"{title_attr} width="{width}" height="{height}" '
                 'style="border:none !important;" '
                 "allowfullscreen webkitallowfullscreen mozallowfullscreen>"
                 "</iframe>"
-            ).format(html=html, width=self.width, height=self.height)
+            ).format(
+                html=html, width=self.width, height=self.height, title_attr=title_attr
+            )
         return iframe
 
     def add_subplot(self, x: int, y: int, n: int, margin: float = 0.05) -> "Div":
@@ -640,6 +648,10 @@ class IFrame(Element):
         height. Values will be converted into pixels in using 60 dpi.
         For example figsize=(10, 5) will result in
         width="600px", height="300px".
+    title : str, default None
+        Value for the iframe's ``title`` attribute, used as the frame's
+        accessible name. Set it to satisfy accessibility audits that
+        require every frame to have an accessible name.
     """
 
     def __init__(
@@ -649,10 +661,12 @@ def __init__(
         height: Optional[str] = None,
         ratio: str = "60%",
         figsize: Optional[Tuple[int, int]] = None,
+        title: Optional[str] = None,
     ):
         super().__init__()
         self._name = "IFrame"
 
+        self.title = title
         self.width = width
         self.height = height
         self.ratio = ratio
@@ -671,21 +685,26 @@ def render(self, **kwargs) -> str:
         html = "data:text/html;charset=utf-8;base64," + base64.b64encode(
             html.encode("utf8"),
         ).decode("utf8")
+        title_attr = f' title="{escape(self.title)}"' if self.title else ""
 
         if self.height is None:
             iframe = (
                 '<div style="width:{width};">'
                 '<div style="position:relative;width:100%;height:0;padding-bottom:{ratio};">'  # noqa
-                '<iframe src="{html}" style="position:absolute;width:100%;height:100%;left:0;top:0;'  # noqa
+                '<iframe src="{html}"{title_attr} style="position:absolute;width:100%;height:100%;left:0;top:0;'  # noqa
                 'border:none !important;">'
                 "</iframe>"
                 "</div></div>"
-            ).format(html=html, width=self.width, ratio=self.ratio)
+            ).format(
+                html=html, width=self.width, ratio=self.ratio, title_attr=title_attr
+            )
         else:
             iframe = (
-                '<iframe src="{html}" width="{width}" style="border:none !important;" '
+                '<iframe src="{html}"{title_attr} width="{width}" style="border:none !important;" '
                 'height="{height}"></iframe>'
-            ).format(html=html, width=self.width, height=self.height)
+            ).format(
+                html=html, width=self.width, height=self.height, title_attr=title_attr
+            )
         return iframe
 
 

tests/test_element.py

@@ -42,3 +42,35 @@ def test_figure_repr_html_fullscreen_attrs_with_height():
         assert name in attrs, f"{name!r} missing; got {sorted(attrs)}"
     assert attrs["height"] == "400px"
     assert attrs["width"] == "100%"
+
+
+def test_figure_iframe_title_absent_by_default():
+    for height in (None, "400px"):
+        attrs = _iframe_attrs(elem.Figure(height=height)._repr_html_())
+        assert "title" not in attrs
+
+
+def test_figure_iframe_title_set():
+    for height in (None, "400px"):
+        attrs = _iframe_attrs(elem.Figure(height=height, title="My Map")._repr_html_())
+        assert attrs["title"] == "My Map"
+
+
+def test_figure_iframe_title_is_escaped():
+    # A title with a double quote must not break out of the attribute.
+    attrs = _iframe_attrs(elem.Figure(title='a "b" <c>')._repr_html_())
+    assert attrs["title"] == 'a "b" <c>'
+
+
+def test_iframe_title_absent_by_default():
+    for height in (None, "300px"):
+        attrs = _iframe_attrs(elem.IFrame("<p>x</p>", height=height).render())
+        assert "title" not in attrs
+
+
+def test_iframe_title_set():
+    for height in (None, "300px"):
+        attrs = _iframe_attrs(
+            elem.IFrame("<p>x</p>", height=height, title="Popup").render()
+        )
+        assert attrs["title"] == "Popup"