In many cases during a debugging session, it is necessary to refer to an environment to establish a frame of reference for identifying variables or statement identifiers. An environment is simply a program block, which the program refers to by specifying the name of the block or any statement within the block. This allows the debugger to find a specific instance of a variable or statement. Usually, a simple block name is adequate to specify an environment. It refers to the most recent activation of that block. To establish some other activation of the block as an environment, use a block activation number.
An active environment exists on the program stack as a stack frame containing automatic data for the environment. However, environments that do not exist on the program stack can also be referenced; such environments are called inactive environments. For example, a procedure that has not been called, and thus has no stack frame, is inactive. Another example of an inactive environment is one that is referenced by a block name followed by an activation number that is higher than the current activation of the block. It is possible to examine static and external data in inactive environments and to set breakpoints in them. An active environment must be specified to examine automatic data or procedure arguments.