Property lists provide a way to associate words with things. Property lists are sometimes called "dictionaries", "associative arrays", or simply "name-value pairs".
Property lists, abbreviated "plists", are always accessed by their name--you can't get at the plist directly. Among other things, this means you cannot pass a plist into a Logo procedure, you can only pass its name.
You can get, set, and remove properties (name-value pairs) from a plist. If you try to get a property that doesn't exist, or you try to get a property from a plist that doesn't exist, you get the empty list. In general, you shouldn't care if a property list exists or not. However, if you do care, you can use PLISTS to get the names of all unburied property lists.
Names of property lists are always case-insensitive. Names of individual properties are case-sensitive or case-insensitive depending on the value of CASEIGNOREDP, which is TRUE by default.