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Search mode shows the whole list of variables, but highlights those that match the search term.
Shadowed variables
A variable is called shadowed if it is redefined later in the node hierarchy. For example, it could be defined at the family level, and then again in a task within that family; in this case, the variable defined in the family is 'shadowed' by the one in the task and will not be used. Shadowed variables are displayed in grey. They can be shown/hidden with the 'VV' button in the Variables panel. By default shadowed variables are visible in the panel.
In the above screenshot, the Family1 and Family variables are taken from the analysis level, not the 0 level, as the analysis node is closer in the hierarchy to the current node.