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Typically, button groups will most frequently be used within tables to group similar actions and decrease the amount of column spacing used by full size buttons
Buttons within this container also tend to be icon only buttons with an accompanying tooltip that explains the path/usage upon hover.
As a guide within table columns, button groups should be used if a single column contains 3 or more actions. For example:
If a column contains 2 buttons; ‘Add’ and ‘Edit’, then use the normal button with word buttons
If a column contains 3 buttons; ‘Add', ‘Edit’ and 'Remove’, then use icon buttons within a button group