Finds the first equivalent value.
For List and SortedSet, returns the node at which the value was found, or
null if no equivalent value exists.
For other collections, returns the index of the found value or -1 if no
equivalent value exists.
Regardless of the collection, the value returned is suitable for passing to
other methods like slice, splice, and swap.
The optional equals argument is alternative for Object.equals.
The optional start is the index from which to begin searching.
Values to the left of the start index will not be considered.
SortedSet, SortedArray, and SortedArraySet do not support overriding the
equals operator nor the start index, and will throw an exception if provided
either.
A meaningful implementation with these parameters may be provided in a future
release.
In version 1, this method is called find, which conflicts with the definition
of find provided by ECMAScript 6.
In version 2, this method is called findValue to eliminate the conflict.
Finds the last equivalent value, searching from the right.
(not implemented) Finds the first value within a collection that passes a test.
(not implemented) Finds the first value within a collection that passes a test. Finds the first index within a collection that passes a test.