[selectors-4] Minor grammar tweaks.

Author: tabatkins

selectors-4/Overview.bs

@@ -3814,18 +3814,18 @@ Appendix B: Obsolete but Required Parsing Quirks for Web Compat</h2>
 			Selectors have long had a behavior
 			where a single unknown/invalid selector
 			invalidates the entire selector list
-			(rather than just invaliding the one complex selector it finds itself in).
+			(rather than just invalidating the one complex selector it finds itself in).
 			This is generally considered a legacy mistake by the WG,
 			but can't be fixed at this point,
 			as too many stylesheets depend on this behavior,
 			intentionally or not.
 
-			One aspect of this is that any use of vendor-specific selectors,
-			which are generally not recognized by other User Agents,
-			invalidate the entire selector,
-			and take the entire style rule down with them.
+			One aspect of this is that use of vendor-specific selectors
+			invalidates the entire selector in other User Agents
+			that don't recognize them,
+			and takes the entire style rule down with it.
 			This has been used intentionally in the past--
-			in the severely not-recommended practice of hiding style rules from some browsers
+			in the severely-not-recommended practice of hiding style rules from some browsers
 			by making them invalid in every other browser--
 			and unintentionally,
 			with people styling an element
@@ -3837,7 +3837,7 @@ Appendix B: Obsolete but Required Parsing Quirks for Web Compat</h2>
 			WebKit-derived user agents,
 			such as Safari or Chrome,
 			have an additional quirk related to their vendor-prefixed pseudo-elements,
-			where any <css>::-webkit-</css>-prefixed selectors is considered valid at parse time.
+			where any <css>::-webkit-</css>-prefixed selectors are considered valid at parse time.
 			(This is probably a leftover quirk of an early CSS feature,
 			since dropped,
 			that intentionally treated all possible pseudo-elements as valid at parse time,
@@ -3848,9 +3848,8 @@ Appendix B: Obsolete but Required Parsing Quirks for Web Compat</h2>
 			this particular vendor-specific oddity has become common enough
 			that other user agents are seeing sites breaking due to them depending on it,
 			accidentally or not.
-			As such, since the quirk is thus,
-			in practical terms,
-			required to render the modern web correctly,
+			As such, since the quirk is in practical terms
+			<em>required</em> to render the modern web correctly,
 			specifying it and requiring it for all user agents
 			ensures that today's web pages are more likely to be correctly rendered
 			in user agents both current and future.