Help text for fractional properties

sandbox/uber.py

@@ -81,6 +81,7 @@ class BasicApp(App):
 
     def action_toggle_border(self):
         self.focused.styles.border = [("solid", "red"), ("dashed", "white")]
+        self.focused.styles.opacity = "x"
 
 
 BasicApp.run(css_file="uber.css", log="textual.log", log_verbosity=1)

src/textual/css/_help_text.py

@@ -526,8 +526,8 @@ def fractional_property_help_text(
                     Bullet(
                         f"In Python, you can set [i]{property_name}[/] to a string or float value",
                         examples=[
-                            Example(f"widget.styles.{property_name} = 0.25"),
                             Example(f'widget.styles.{property_name} = "50%"'),
+                            Example(f"widget.styles.{property_name} = 0.25"),
                         ],
                     )
                 ],
@@ -535,11 +535,11 @@ def fractional_property_help_text(
                     Bullet(
                         f"In Textual CSS, you can set [i]{property_name}[/] to a string or float",
                         examples=[
-                            Example(f"{property_name}: 0.25;"),
                             Example(f"{property_name}: 50%;"),
+                            Example(f"{property_name}: 0.25;"),
                         ],
                     )
                 ],
-            )
+            ).get_by_context(context)
         ],
     )

src/textual/css/_style_properties.py

@@ -14,7 +14,11 @@ from typing import Iterable, NamedTuple, TYPE_CHECKING, cast
 import rich.repr
 from rich.style import Style
 
-from ._help_text import border_property_help_text, layout_property_help_text
+from ._help_text import (
+    border_property_help_text,
+    layout_property_help_text,
+    fractional_property_help_text,
+)
 from ._help_text import (
     spacing_wrong_number_of_values,
     scalar_help_text,
@@ -908,8 +912,9 @@ class FractionalProperty:
         elif isinstance(value, str) and value.endswith("%"):
             float_value = float(Scalar.parse(value).value) / 100
         else:
-            raise StyleTypeError(
-                f"{self.name} must be a str (e.g. '10%') or a float (e.g. 0.1)"
+            raise StyleValueError(
+                f"{self.name} must be a str (e.g. '10%') or a float (e.g. 0.1)",
+                help_text=fractional_property_help_text(name, context="inline"),
             )
         if obj.set_rule(name, clamp(float_value, 0, 1)):
             obj.refresh()

src/textual/css/_styles_builder.py

@@ -16,6 +16,7 @@ from ._help_text import (
     layout_property_help_text,
     docks_property_help_text,
     dock_property_help_text,
+    fractional_property_help_text,
 )
 from .constants import (
     VALID_ALIGN_HORIZONTAL,
@@ -315,13 +316,7 @@ class StylesBuilder:
                 error = True
 
         if error:
-            self.error(
-                name,
-                token,
-                f"property 'opacity' has invalid value {_join_tokens(tokens)!r}; "
-                f"expected a percentage or float between 0 and 1; "
-                f"example valid values: '0.4', '40%'",
-            )
+            self.error(name, token, fractional_property_help_text(name, context="css"))
 
     def _process_space(self, name: str, tokens: list[Token]) -> None:
         space: list[int] = []