Enforce required attributes and establish :keywords: as required (#839)

Author: sarahlwelton

home/modules/contribute/pages/attributes-and-roles.adoc

@@ -45,12 +45,14 @@ In this case, the tabs feature is turned on by setting `tabs`.
 <5> Reference an attribute in the body of the document by entering the attribute name inside a set of curly brackets (`+{attribute-name}+`).
 <6> Code blocks are assigned the source language `javascript`.
 
-== Available Document Attributes 
+== Required Document Attributes 
 
 The following document attributes must be included for every AsciiDoc file stored in a *pages* directory: 
 
 include::partial$available-attributes.adoc[tag=required]
 
+== Optional Document Attributes
+
 You can also use the following optional attributes: 
 
 include::partial$available-attributes.adoc[tag=optional]

home/modules/contribute/partials/available-attributes.adoc

@@ -10,6 +10,10 @@ a| * For concepts: `concept`
 * For tasks: `guide`
 * For references: `reference`
 
+| `:keywords:`
+| Use the `keywords` attribute to add meta keywords to the HTML head for your page. 
+| Any applicable keyword, separated by commas (`,`).
+
 | `:description:` 
 | The page description is used for SEO and provides a brief description of the page, which is displayed using the `[abstract]` attribute on the page. 
 a| Enter a quick description of the content on the page.
@@ -38,10 +42,6 @@ a| `:imagesdir: ../assets/images`
 
 Try to keep your images inside the `assets/images` folder in a module.
 
-| `:keywords:`
-| Use the `keywords` attribute to add meta keywords to the HTML head for your page. 
-| Any applicable keyword, separated by commas (`,`).
-
 | `:page-aliases:` 
 a| Use the `page-aliases` attribute when you need to delete or rename a page to avoid breaking links.
 Antora will resolve any links to the filename(s) you specify in this attribute to redirect to the current page, instead.