[css-highlight] Avoid use of RFC2119 keywords in non normative text

Author: frivoal

css-highlight-api-1/Overview.bs

@@ -472,11 +472,11 @@ Highlight types</h4>
 	A custom highlight will have a default type of {{HighlightType/highlight}}
 	if its {{Highlight/type}} attribute has not been explicitly set.
 
-	Note: Authors should set a [=custom highlight=]'s {{Highlight/type}} to {{HighlightType/spelling-error}}
+	Note: Authors are advised to set a [=custom highlight=]'s {{Highlight/type}} to {{HighlightType/spelling-error}}
 	when that [=custom highlight=] is being used to emphasize misspelled content.
-	Authors should set a [=custom highlight=]'s {{Highlight/type}} to {{HighlightType/grammar-error}}
+	Authors are advised to set a [=custom highlight=]'s {{Highlight/type}} to {{HighlightType/grammar-error}}
 	when that [=custom highlight=] is being used to emphasize content that is grammatically incorrect.
-	For all other use cases {{Highlight/type}} should be left as {{HighlightType/highlight}}.
+	For all other use cases {{Highlight/type}} is best left as {{HighlightType/highlight}}.
 
 	UAs should make [=custom highlight=]s available to assistive technologies.
 	When exposing a highlight using a given platform accessibility API,
@@ -486,20 +486,20 @@ Highlight types</h4>
 
 	Note: For example,
 	if a platform accessibility API has the capability to express spelling errors and grammar errors specifically,
-	then UAs should use these capabilities to convey the semantics for highlights
+	then UAs is expected to use these capabilities to convey the semantics for highlights
 	with {{HighlightType/spelling-error}} and {{HighlightType/spelling-error}}.
 	If an accessibility API only has the capability to express spelling errors,
-	then UAs should convey both highlights with {{HighlightType/spelling-error}}
+	then UAs would be expected to convey both highlights with {{HighlightType/spelling-error}}
 	and with {{HighlightType/grammar-error}} using spelling error semantics.
 	If an accessibility API has support for expressing neither spelling errors nor grammar errors,
-	then UAs should expose all highlights as generic {{HighlightType/highlight}} regardless of their actual {{Highlight/type}}.
+	then UAs would expose all highlights as generic {{HighlightType/highlight}} regardless of their actual {{Highlight/type}}.
 
 	Note: This initial set of types was chosen
 	because they are expected to be popular use cases for Highlight API
 	and there is some existing support for expressing their semantics in platform accessibility APIs today.
 	Accessibility APIs currently don't have any way to express the specific semantics
 	of other expected Highlight API use cases.
-	More types may be added to {{HighlightType}}
+	More types could later be added to {{HighlightType}}
 	as accessibility APIs gain support for expressing additional popular use cases of Highlight API.
 
 <h2 id=responding-to-changes>