docstring and test

src/textual/content.py

@@ -396,12 +396,14 @@ class Content(Visual):
         return cls("".join(text), spans)
 
     def simplify(self) -> Content:
-        """Simplify spans in place.
+        """Simplify spans by joining contiguous spans together.
 
-        This joins contiguous spans together which can produce faster renders.
+        This can produce faster renders but typically only worth it if you have appended a
+        large number of Content instances together.
 
-        Note that this is only typically worth it if you have appended a large number of Content instances together,
-        and it only needs to be done once.
+        Note that this this modifies the Content instance in-place, which might appear
+        to violate the immutability constraints, but it will not change the rendered output,
+        nor its hash.
 
         Returns:
             Self.

tests/test_content.py

@@ -286,3 +286,11 @@ def test_split_and_tabs():
     content = Content("--- hello.py\t2024-01-15 10:30:00.000000000 -0800", spans=spans)
     widget = Widget()
     content.render_strips(0, None, Style(), RenderOptions(widget._get_style, {}))
+
+
+def test_simplify():
+    """Test simplify joins spans."""
+    content = Content.from_markup("[bold]Foo[/][bold]Bar[/]")
+    assert content.spans == [Span(0, 3, "bold"), Span(3, 6, "bold")]
+    content.simplify()
+    assert content.spans == [Span(0, 6, "bold")]