DPANS94

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## A.2 Terms and notation

### A.2.1 Definitions of terms

ambiguous condition
  The response of a Standard System to an ambiguous condition is left to the discretion of the implementor. A Standard System need not explicitly detect or report the occurrence of ambiguous conditions.

cross compiler
  Cross-compilers may be used to prepare a program for execution in an embedded system, or may be used to generate Forth kernels either for the same or a different run-time environment.

data field
  In earlier standards, data fields were known as parameter fields.

  On subroutine threaded Forth systems, everything is object code. There are no traditional code or data fields. Only a word defined by CREATE or by a word that calls CREATE has a data field. Only a data field defined via CREATE can be manipulated portably.

word set
  This Standard recognizes that some functions, while useful in certain application areas, are not sufficiently general to justify requiring them in all Forth systems. Further, it is helpful to group Forth words according to related functions. These issues are dealt with using the concept of word sets.

  The Core word set contains the essential body of words in a Forth system. It is the only required word set. Other word sets defined in this Standard are optional additions to make it possible to provide Standard Systems with tailored levels of functionality.

### A.2.2 Notation

#### A.2.2.2 Stack notation

The use of -sys, orig, and dest data types in stack effect diagrams conveys two pieces of information. First, it warns the reader that many implementations use the data stack in unspecified ways for those purposes, so that items underneath on either the control-flow or data stacks are unavailable. Second, in cases where orig and dest are used, explicit pairing rules are documented on the assumption that all systems will implement that model so that its results are equivalent to employment of some stack, and that in fact many implementations do use the data stack for this purpose. However, nothing in this Standard requires that implementations actually employ the data stack (or any other) for this purpose so long as the implied behavior of the model is maintained.

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