This class allows you to create and manipulate dialog windows on the user interface. You can use this class to display messages, forms, or custom HTML content in a modal window.
GuideAjex: This class allows you to make asynchronous calls to the server and process the response. You can use this class to retrieve data, execute scripts, or perform actions on the server without reloading the page.
GuideForm: This class allows you to access and manipulate the fields and values on a form. You can use this class to get or set field values, show or hide fields, add or remove options, or validate field inputs.
The class GuideRecord is not part of the Client side scoped APIs. GuideRecord is part of the Server side scoped APIs, which are a set of classes and methods that allow you to interact with the database and perform server-side logic on the ServiceNow platform. GuideRecord is a class that represents a record in a table and allows you to query, insert, update, or delete records on the server.
Reference:
[Client side scoped APIs]
[Server side scoped APIs]

"Application developers must select an application as their current scope context." https://docs.servicenow.com/bundle/tokyo-application-development/page/build/applications/task/t_SelectAnAppFromTheAppPicker.html

Checkbox tooltip: "Show this module when the user has the specified roles. Otherwise the user must have the roles specified by both the application menu and the module." The following is true for the Override application menu roles configuration option when configuring a module:
Users with the module role but without access to the application menu access the module. This is true because the Override application menu roles option allows users to bypass the application menu role requirement and access the module directly if they have the module role. For example, if a module has the itil role and the Override application menu roles option enabled, and the application menu has the admin role, then a user who has the itil role but not the admin role can still access the module.
The following are not true for the Override application menu roles configuration option when configuring a module:
Self-Service users can access the module even though they do not have roles. This is false because the Override application menu roles option does not grant access to the module to users who do not have any roles. Self-Service users are users who do not have any roles assigned to them and can only access the Self-Service portal and the Knowledge Base. To access the module, users need to have at least the module role.
Admin is given access to the module even if Access Controls would ordinarily prevent access. This is false because the Override application menu roles option does not override the Access Control (ACL) rules that apply to the module. Access Control rules are used to restrict the access to the data and functionality of the ServiceNow platform based on the user's roles and conditions. Admin is a role

https://docs.servicenow.com/bundle/tokyo-application-development/page/script/server-scripting/concept/c_ServerScripting.html

https://developer.servicenow.com/dev.do#!/reference/api/rome/client
The GlideUser object (g_user) is part of the client-side scripting API that provides information about the current user and the user's preferences. It can be used in Client Scripts and UI Policies to customize the user interface based on the user's role, language, time zone, etc. The workflow.scratchpad object is only available in Workflow scripts, which are used to automate processes on the platform. The current and previous objects are only available in server-side scripts, such as Business Rules and Script Includes. The GlideSystem object (gs) is also a server-side object that provides methods for logging, debugging, date and time calculations, etc.
Reference:
[GlideUser object (g_user)]
[Workflow scripts]
[Business Rules]
Script Includes
[GlideSystem object (gs)]