Improve B0004 warning description

Author: nicopap

crates/bevy_hierarchy/src/valid_parent_check_plugin.rs

@@ -70,7 +70,7 @@ where
 /// which parent hasn't a `T` component.
 ///
 /// See [`check_hierarchy_component_has_valid_parent`] for details.
-pub struct ValidParentCheckPlugin<T>(PhantomData<fn() -> T>);
+pub struct ValidParentCheckPlugin<T: Component>(PhantomData<fn() -> T>);
 impl<T: Component> Default for ValidParentCheckPlugin<T> {
     fn default() -> Self {
         Self(PhantomData)

errors/B0004.md

@@ -5,12 +5,19 @@ A runtime warning.
 An [`Entity`] with a hierarchy-inherited component has a [`Parent`]
 without the hierarchy-inherited component in question.
 
-The hierarchy-inherited components are:
+The hierarchy-inherited components defined in bevy include:
 
 - [`ComputedVisibility`]
 - [`GlobalTransform`]
 
-For example, the following code will cause a warning to be emitted:
+Third party plugins may also define their own hierarchy components, so
+read carefully the warning message and pay attention to the exact type
+of the missing component.
+
+To fix this warning, add the missing hierarchy component to all ancestors
+of entities with the hierarchy component you wish to use.
+
+The following code will cause a warning to be emitted:
 
 ```rust,no_run
 use bevy::prelude::*;
@@ -55,7 +62,7 @@ Since the cube is spawned as a child of an entity without the
 [`ComputedVisibility`] component, it will not be visible at all.
 
 To fix this, you must use [`SpatialBundle`] over [`TransformBundle`],
-as follow:
+as follows:
 
 ```rust,no_run
 use bevy::prelude::*;
@@ -100,7 +107,7 @@ However, when a parent [`GlobalTransform`] is missing,
 it will simply prevent all transform propagation,
 including when updating the [`Transform`] component of the child.
 
-You will most likely encouter this warning when loading a scene
+You will most likely encounter this warning when loading a scene
 as a child of a pre-existing [`Entity`] that does not have the proper components.
 
 [`ComputedVisibility`]: https://docs.rs/bevy/*/bevy/render/view/struct.ComputedVisibility.html