Add 'front matter' to Vale substitution rules

Also improves wording of sentence.

doc/.vale/gitlab/Substitutions.yml

@@ -9,6 +9,7 @@ link: https://about.gitlab.com/handbook/communication/#top-misused-terms
 level: error
 ignorecase: true
 swap:
+  frontmatter: front matter
   GitLabber: GitLab team member
   gitlab omnibus: Omnibus GitLab
   param: parameter

doc/development/documentation/index.md

@@ -550,7 +550,7 @@ You can also
 [configure the text editor of your choice](https://errata-ai.github.io/vale/#local-use-by-a-single-writer)
 to display the results.
 
-Vale's test results [are displayed](#testing) in CI pipelines.
+Vale's error-level test results [are displayed](#testing) in CI pipelines.
 
 ##### Disable a Vale test
 

doc/development/documentation/site_architecture/index.md

@@ -173,7 +173,7 @@ we reference the array with a symbol (`:versions`).
 ## Bumping versions of CSS and JavaScript
 
 Whenever the custom CSS and JavaScript files under `content/assets/` change,
-make sure to bump their version in the frontmatter. This method guarantees that
+make sure to bump their version in the front matter. This method guarantees that
 your changes will take effect by clearing the cache of previous files.
 
 Always use Nanoc's way of including those files, do not hardcode them in the

doc/user/project/description_templates.md

@@ -29,7 +29,7 @@ templates of the default branch will be taken into account.
   For example, if you have a project for tracking new blog posts, you can require the
   title, outlines, author name, author social media information, and so on.
 - Following the previous example, you can make a template for every MR submitted
-  with a new blog post, requiring information about the post date, frontmatter data,
+  with a new blog post, requiring information about the post date, front matter data,
   images guidelines, link to the related issue, reviewer name, and so on.
 - You can also create issues and merge request templates for different
   stages of your workflow, for example, feature proposal, feature improvement, or a bug report.