In Deriscope terminology, a Key is a text label that ends with the suffix = and serves as a parameter label in a context when a function expects several parameters as input or returns several parameters as output.
In fact, the input or output data of some function are essentially a collection of Keys and
In the special case of the function , the corresponding Keys may be also generally seen as labels of the constituents of the object produced by that function.
There exist intuitive rules that identify which corresponds to each Key.
For example, in Excel the pair consisting of the Key Maturity= and the corresponding Value 22-July-2040 can be represented by a two-cell range of which the left cell contains the text Maturity= and the right cell containes the date 22-July-2040
Then this two-cell range can be part of the input to some function that expects the key Maturity= as a label for the maturity parameter.
Then that function will parse the supplied pair Maturity= 22-July-2040 and identify the date 22-July-2040 as the date to be used as maturity.
For example, such a function is the Create of the Zero Bond, which interpretes the value accompanying the Key Maturity= as the maturity date of the zero bond instrument.