Peek mode works by setting a flag in the instance descriptor of a subcell. Instance descriptors are stored in the parent cell. Suppose that a design contains multiple instances of cell B, each of which contains a left and right instance of cell A. In peek mode, for example, if the left instance of A is made to be expanded in an instance of B (which of course is also expanded), this expansion of A will appear in all instances of B which are expanded, not just the one clicked on. This is a consequence of the hierarchical nature of the database, where each instance of B represents the contents of B, which includes the instance of A with the flag set.
In peek mode, the operation applies to any window in which the pointer was located when button one was pressed. The result will be consistent with the expansion depth of the particular window. While in peek mode, certain keyboard commands can be applied, which will affect the window where the pointer was located when the key press occurred. The + and - keys increment and decrement the expansion depth, a number key will set the expansion depth, a will set the depth to ``all'', and n will set the depth to ``none'', as will 0 (zero). Each window has independent expansion parameters. Setting the expansion depth to zero by pressing 0 or n will clear the peek mode display flags. Otherwise, the expansion depth and the peek mode display of cells are independent.
In electrical mode, symbolic cells can be shown as expanded, with a miniature rendition of the actual circuit inside the symbolic bounding box area, in peek mode. Click on the symbolic cell to expand, Shift-click to unexpand. Wires connecting the circuit connections to the symbol terminals are added. This rendition is for visual purposes only. If a subcell placed in symbolic mode is later changed to non-symbolic mode, the view of the parent cell is likely to look horrid, since the subcircuits will probably overlap. The peek mode feature allows viewing of the underlying circuit without this problem.
The expansion status of a given subcell in a window is retained after exiting peek mode, and after canceling a sub-window. Setting the expansion to ``none'' clears all expansion in peek mode.