The Expression Editor will simplify the readability of expressions as it checks for inconsistencies and helps you with some guidance and basic validations to create the expression.
Note, the Visible option is not always available, it depends on the context expression is used, e.g. it is useful when writing expressions for map Info panel. The Functions context menu options will show all the available Expression Functions and they are inserted in Expression field as they are selected.

Hotkeys

CTRL + SPACE Reveal Functions & Variables Menu
CTRL + G $GET function (common function to return a value from given path)
CTRL + I @item (the source object)
CTRL + N ”name” (common attribute)
CTRL + R @record
Variables – Verso View will give the list of available default variables, user defined variables and dataset(s) as input to new Expression Variables in view; Example that shows the available items defined in view

Refresh this menu

Sometimes the contents of the context menu are not updated, especially for some Variables and Datasets that require calculations to be updated, hence the Refresh option to update the list.
While configuring the World Map, additional options are available – the fields that was fetched from the Layer URL; Example showing the available fields from Layer to be used in an expression and also the items that are referenced by the Source setting for World Map; Example that shows the available items to be used in an expression, in this case a filter box that list Countries from the Geographical Area domain. The status bar at the bottom of Expression Editor will provide a possible cause of error in expression. The expression will also be marked with red color as seen in the examples below; Example 1, missing parenthesis Example 2, wrong symbol in front of expression function Example 3, no error, and as one can see the parenthesis is being paired for better readability

Web Expression Editor

Hotkeys
CTRL + G $GET(@item,)
CTRL + I @item
CTRL + SPACE Reveal menu with available functions and  variables