Better headings - SEO

- Improve clarity and SEO "GitLab Pages **default** domain names"
- Headings in sentence case

doc/user/group/subgroups/index.md

@@ -176,7 +176,7 @@ Here's a list of what you can't do with subgroups:
 - [GitLab Pages](../../project/pages/index.md) supports projects hosted under
   a subgroup, but not subgroup websites.
   That means that only the highest-level group supports
-  [group websites](../../project/pages/getting_started_part_one.md#gitlab-pages-domain-names),
+  [group websites](../../project/pages/getting_started_part_one.md#gitlab-pages-default-domain-names),
   although you can have project websites under a subgroup.
 - It is not possible to share a project with a group that's an ancestor of
   the group the project is in. That means you can only share as you walk down

doc/user/project/pages/getting_started/new_or_existing_website.md

@@ -14,7 +14,7 @@ To do so, follow the steps below.
 
 1. From your **Project**'s **[Dashboard](https://gitlab.com/dashboard/projects)**,
    click **New project**, and name it according to the
-   [Pages domain names](../getting_started_part_one.md#gitlab-pages-domain-names).
+   [Pages domain names](../getting_started_part_one.md#gitlab-pages-default-domain-names).
 1. Clone it to your local computer, add your website
    files to your project, add, commit and push to GitLab.
    Alternativelly, you can run `git init` in your local directory,

doc/user/project/pages/getting_started_part_one.md

@@ -8,7 +8,7 @@ type: concepts, reference
 On this document, learn how to name your project for GitLab Pages
 according to your intended website's URL.
 
-## GitLab Pages domain names
+## GitLab Pages default domain names
 
 >**Note:**
 If you use your own GitLab instance to deploy your
@@ -80,7 +80,7 @@ To understand Pages domains clearly, read the examples below.
 - On your GitLab instance, replace `gitlab.io` above with your
   Pages server domain. Ask your sysadmin for this information.
 
-## URLs and Baseurls
+## URLs and baseurls
 
 Every Static Site Generator (SSG) default configuration expects
 to find your website under a (sub)domain (`example.com`), not
@@ -108,7 +108,7 @@ example we've just mentioned, you'd have to change Jekyll's `_config.yml` to:
 baseurl: ""
 ```
 
-## Custom Domains
+## Custom domains
 
 GitLab Pages supports custom domains and subdomains, served under HTTP or HTTPS.
 See [GitLab Pages custom domains and SSL/TLS Certificates](custom_domains_ssl_tls_certification/index.md) for more information.

doc/user/project/pages/index.md

@@ -83,7 +83,7 @@ to build your site and publish it to the GitLab Pages server. The sequence of
 scripts that GitLab CI/CD runs to accomplish this task is created from a file named
 `.gitlab-ci.yml`, which you can [create and modify](getting_started_part_four.md) at will. A specific `job` called `pages` in the configuration file will make GitLab aware that you are deploying a GitLab Pages website.
 
-You can either use GitLab's [default domain for GitLab Pages websites](getting_started_part_one.md#gitlab-pages-domain-names),
+You can either use GitLab's [default domain for GitLab Pages websites](getting_started_part_one.md#gitlab-pages-default-domain-names),
 `*.gitlab.io`, or your own domain (`example.com`). In that case, you'll
 need admin access to your domain's registrar (or control panel) to set it up with Pages.