A tag is a string that you can associate with objects on the canvas.
A tag can be associated with any number of objects on the canvas, including zero.
An object can have any number of tags associated with it, including zero.
Tags have many uses. For example, if you are
drawing a map on a canvas, and there are text objects
for the labels on rivers, you could attach the tag
'riverLabel' to all those text
objects. This would allow you to perform operations on
all the objects with that tag, such as changing their
color or deleting them.