Describe what setInternal does

API page: https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21TypedData...

There are no docs on what "setInternal" or "internal" property does.

Some info is here: https://www.drupal.org/node/2916592 but far from complete explanation.

Proposed resolution

Add more information about the internal property:

/**
   * Sets the whether the data value should be internal.
   *
   * Internal fields and properties should not be exposed to outside
   * systems.
   *
   * This can be used in a scenario when it is not desirable to expose data of
   * this entity type to an external system.
   *
   * The implications of this method are left to the discretion of the caller.
   * For example, a module providing an HTTP API may not expose entities of
   * this type or a custom entity reference field settings form may 
   * deprioritize entities of this type in a select list.

Remaining tasks

1. Write patch
2. Review and confirm documentation change is accurate

User interface changes

N/A

API changes

N/A

Data model changes

N/A

Release notes snippet

N/A