PSL fully implements the powerful M local storage tree (array) structure.
PSL assumes that nodes at a particular subscript level are homogenous. That is, each node is supposed to contain objects of the same type.
Although PSL does not make any assumptions about the values that are used as subscripts, it is recommended to restrict subscripts to values of the Number class and the String class.
Example
type RecordDEP depArray() // Array of DEP records
type Cache %CACHE() // Array of Cache objects
type RecordACN acnArray() // Can contain DEP and LN too
type String calls(,,) // With 3 subscript levels