Add clarity to WPMS documentation about requesting multisites

source/content/guides/custom-upstream/01-custom-upstream.md

@@ -126,20 +126,38 @@ Support for Custom Upstreams requires that the externally hosted upstream reposi
 
 Here are definitions for commonly used terms:
 
-- **Upstream**: A repository that acts as a parent for another repository, like [Pantheon's WordPress Upstream](https://github.com/pantheon-systems/wordpress). The next two definitions are specific types of Upstreams.
+### Upstream
 
-- **Custom Upstream**: A repository restricted to members of an organization, containing a common codebase for new sites. This type of repository is a child repository to Pantheon's core upstreams ([WordPress](https://github.com/pantheon-systems/wordpress),[Drupal (Latest Version)](https://github.com/pantheon-upstreams/drupal-composer-managed), [Drupal 7](https://github.com/pantheon-systems/drops-7)) and acts as a parent for site level repositories.
+<p>An <dfn id="upstream">upstream</dfn> is a repository that acts as a parent for another repository, like <a href="https://github.com/pantheon-systems/wordpress">Pantheon's WordPress Upstream</a>.</p>
 
-- **Public Upstream**: A repository that is open to all Pantheon users which contains a common codebase for new sites, like [Panopoly](https://github.com/populist/panopoly-drops-7).
+### Custom Upstream
 
-- **Repository**: A collection of files packaged in a single directory under version control.
+<p>A <dfn id="custom-upstream">custom upstream</dfn> is a repository restricted to members of an organization, containing a common codebase for new sites. This type of repository is a child repository to Pantheon's core upstreams (<a href="https://github.com/pantheon-systems/wordpress">WordPress</a>, <a href="https://github.com/pantheon-upstreams/drupal-composer-managed">Drupal (Latest Version)</a>, <a href="https://github.com/pantheon-systems/drops-7">Drupal 7</a>) and acts as a parent for site level repositories.</p>
 
-- **Remote Repository**: A central version control location, such as a repository residing on GitHub, Bitbucket, or GitLab.
+### Public Upstream
 
-- **Upstream Updates**: Code changes that are made once in a parent (upstream) repository, then applied "downstream" to child repositories. This is how Pantheon's one-click updates work.
+<p>A <dfn id="public-upstream">public upstream</dfn> is a repository that is open to all Pantheon users which contains a common codebase for new sites, like <a href="https://github.com/populist/panopoly-drops-7">Panopoly</a>.</p>
 
-- **Site Repository**: Child repository where upstream updates are applied and site specific customizations are tracked, similar to your site's codebase on Pantheon.
+### Repository
 
+<p>A<dfn id="repository">repository</dfn> is a collection of files packaged in a single directory under version control.</p>
+
+
+### Remote Repository
+
+<p>A <dfn id="remote-repository">remote repository</dfn> is the central version control location, such as a repository residing on GitHub, Bitbucket, or GitLab.</p>
+
+### Upstream Updates
+
+<p><dfn id="upstream-updates"> Upstream Updates</dfn> are code changes that are made once in a parent (upstream) repository, then applied "downstream" to child repositories. This is how Pantheon's one-click updates work.</p>
+
+### Site Repository
+
+<p>A <dfn id="site-repository">site repository</dfn> is a child repository where upstream updates are applied and site specific customizations are tracked, similar to your site's codebase on Pantheon.</p>
+
+### Framework
+
+<p>The <dfn id="upstream-framework">upstream framework</dfn> (or site framework) determines the server configuration for a given CMS. It includes things like Nginx configuration, the relevant CLI tool to install (Drush or WP-CLI), etc. This setting is <em>not visible</em> to users and once a framework has been set for a site (based on how the upstream was configured), it cannot be changed without <a href="https://docs.pantheon.io/guides/custom-upstream/switch-custom-upstream">changing the upstream</a> itself.</p>
 
 ## More Resources
 

source/content/guides/multisite/01-introduction.md

@@ -41,17 +41,19 @@ We do not support uses of WordPress Multisite that run functionally-different or
 ## Request a WordPress Multisite
 WordPress Multisite requires a special configuration that is only available to select customers. Access to WordPress Multisite requires a Gold, Platinum, or Diamond level [Workspace plan](https://pantheon.io/plans/pricing).
 
-By default, Pantheon employees must create new Multisites on your behalf. Reach out to your account manager to request site creation for a new WordPress Multisite.
+By default, Pantheon employees must create new Multisites on your behalf. This is because they use a different site [framework](/glossary/#upstream-framework) (which includes server settings like Nginx configuration) than the default `wordpress` framework typically available to customers. Reach out to your account manager to request site creation for a new WordPress Multisite.
 
 If you want to create new WordPress Multisites self-serve and on-demand in the Pantheon Dashboard, reach out to your account manager and request a [Custom Upstream](/guides/custom-upstream) for your workspace based on Pantheon's WordPress Multisite framework.
 
-Existing WordPress sites cannot be converted to a multisite, however they can be [migrated](/migrate-wordpress-multisite).
+Setting up an existing WordPress site  on Pantheon as a WordPress multisite without the correct framework can result in unexpected errors due to the improper Nginx configuration. If you have an existing WordPress site that you want to make into a multisite but the upstream does not use the `wordpress_network` framework (visible in the Pantheon Dashboard), and a WordPress Multisite upstream has been created for you, you can create a new site based on that upstream and push your codebase pushed to the new site repository (since WordPress Multisite is a core component of WordPress and uses the same code).
 
 If you don't have an account manager, you can [contact sales](https://pantheon.io/contact-us).
 
 
  ## More Resources
 
+- [Migrate a WordPress Multisite onto Pantheon](/migrate-wordpress-multisite)
+
 - [WordPress on Pantheon Quick Start Guide](/guides/wordpress-pantheon/)
 
 - [Supported WordPress Versions](/supported-wp)