Lenient markup

CHANGELOG.md

@@ -17,6 +17,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 - Added experimental opt-in support for https://github.com/willmcgugan/textual-speedups
 
+### Changed
+
+- Content markup is now more lenient; if a 'tag' doesn't contain a valid style it will be included verbatim. https://github.com/Textualize/textual/pull/5851
+
 ## [3.3.0] - 2025-06-01
 
 ### Fixed

src/textual/markup.py

@@ -48,8 +48,9 @@ class MarkupError(Exception):
         variable_ref=VARIABLE_REF,
         whitespace=r"\s+",
     )
-    .expect_eof(False)
+    .expect_eof(True)
     .expect_semicolon(False)
+    .extract_text(True)
 )
 
 expect_markup = Expect(
@@ -374,14 +375,36 @@ def process_text(template_text: str, /) -> str:
         elif token_name == "open_tag":
             tag_text = []
 
+            eof = False
+            contains_text = False
             for token in iter_tokens:
                 if token.name == "end_tag":
                     break
+                elif token.name == "text":
+                    contains_text = True
+                elif token.name == "eof":
+                    eof = True
                 tag_text.append(token.value)
-            opening_tag = "".join(tag_text).strip()
-            style_stack.append(
-                (position, opening_tag, normalize_markup_tag(opening_tag))
-            )
+            if contains_text or eof:
+                # "tag" was unparsable
+                text_content = f"[{''.join(tag_text)}" + ("" if eof else "]")
+                text_append(text_content)
+                position += len(text_content)
+            else:
+                opening_tag = "".join(tag_text)
+
+                if not opening_tag.strip():
+                    blank_tag = f"[{opening_tag}]"
+                    text_append(blank_tag)
+                    position += len(blank_tag)
+                else:
+                    style_stack.append(
+                        (
+                            position,
+                            opening_tag,
+                            normalize_markup_tag(opening_tag.strip()),
+                        )
+                    )
 
         elif token_name == "open_closing_tag":
             tag_text = []

tests/test_content.py

@@ -229,6 +229,7 @@ def test_assemble():
         ("\\[/foo", "[/foo"),
         ("\\[/foo]", "[/foo]"),
         ("\\[]", "[]"),
+        ("\\[0]", "[0]"),
     ],
 )
 def test_escape(markup: str, plain: str) -> None:
@@ -273,14 +274,3 @@ def test_first_line():
     first_line = content.first_line
     assert first_line.plain == "foo"
     assert first_line.spans == [Span(0, 3, "red")]
-
-
-def test_errors():
-    with pytest.raises(Exception):
-        Content.from_markup("[")
-
-    with pytest.raises(Exception):
-        Content.from_markup("[:")
-
-    with pytest.raises(Exception):
-        Content.from_markup("[foo")

tests/test_markup.py

@@ -10,6 +10,15 @@
     ["markup", "content"],
     [
         ("", Content("")),
+        ("[", Content("[")),
+        ("[]", Content("[]")),
+        ("[ ", Content("[ ")),
+        ("[  ", Content("[  ")),
+        ("[  ]", Content("[  ]")),
+        ("[0", Content("[0")),
+        ("[0]", Content("[0]")),
+        ("[red", Content("[red")),
+        ("[red]", Content("")),
         ("foo", Content("foo")),
         ("foo\n", Content("foo\n")),
         ("foo\nbar", Content("foo\nbar")),
@@ -152,8 +161,6 @@ def test_to_content(markup: str, content: Content):
 
 
 def test_content_parse_fail() -> None:
-    with pytest.raises(MarkupError):
-        to_content("[rgb(1,2,3,4)]foo")
     with pytest.raises(MarkupError):
         to_content("[foo]foo[/bar]")
     with pytest.raises(MarkupError):