Update guidance to emphasise importance of error messages on grouped …

…inputs

src/components/date-input/index.md.njk

@@ -53,11 +53,11 @@ You will not normally need to use the `autocomplete` attribute in prototypes, as
 
 ### Error messages
 
-Error messages should be styled like this if you’re highlighting the date as a whole:
+If you’re highlighting the date as a whole, style all of the fields like this:
 
 {{ example({group: "components", item: "date-input", example: "error", html: true, nunjucks: true, open: false, size: "m"}) }}
 
-Or like this is you’re highlighting just one of the day, month or year:
+If you’re highlighting just one of the day, month or year, only style the field with an error. The error message must clearly state which field has an error.
 
 {{ example({group: "components", item: "date-input", example: "error-single", html: true, nunjucks: true, open: false, size: "m"}) }}
 

src/components/error-message/index.md.njk

@@ -35,7 +35,7 @@ For each error:
 
 - put the message in red after the question text and hint text
 - use a red border to visually connect the message and the question it belongs to
-- if the error relates to specific text fields within the question, give these a red border as well
+- if the error relates to a specific field within the question, give the field a red border and refer to it clearly in the error message
 
 To help screen reader users, the error message component includes a hidden 'Error:' before the error message. These users will hear, for example, "Error: The date your passport was issued must be in the past".