In general, different libraries are completely separate collections of cells that do not relate. For example, two cells in different libraries can have the same name without being the same size or having the same content. Although a cell from one library can be used as an instance in another, this causes the two libraries to be linked together. It may be simpler to copy the cells from one library to another, thus allowing a single library to contain the entire design.

A simple way to copy cells from one library to another is to drag them in the Explorer window (see Section 4-5-2).

A more powerful method is the Cross-Library Copy... command (in menu Cell). This command provides a dialog for copying cells between libraries. The left and right columns show the contents of two different libraries (and the pulldowns above each column let you select the two libraries that you want to see).

When there is a cell with the same name in both libraries, the system compares them to determine which is newer. If you check "Date and content" (and then "Compare" to do comparison again) Electric will compare the actual contents of cells when determining their equality. Unchecking "Examine quietly" will cause the system to describe differences found during comparison.

By choosing one or more cells in the right-hand library and clicking "<< Copy", those cells are copied into the left-hand library. The "Copy >>" button does the reverse. If "Delete after copy" is checked, the buttons change to "<< Move" and "Move >>".

The system can be requested to copy additional cells that relate to the selected one. By checking "Copy subcells", all subcells of the copied cell are also transferred. By checking "Copy all related views", all related views (icon, schematic, layout, etc.) are also transferred. Note that if "Copy all related views" is off but you want to "Copy subcells", it still copies related views in a limited fashion (i.e. schematics and icons are copied together).

When there is a reference to an instance inside of a copied cell, and that instance already exists in the destination library, there are many ways to handle the transfer. For example, library "Frank" has cell "A" which has, inside of it, an instance of cell "B" ("B" is also in library "Frank"). You want to copy cell "A" to library "Tom", but there is already a cell called "B" in library "Tom". These things may happen:

- If "Copy subcells" is checked, then a new version of "Tom:B" is created from "Frank:B", and this cell is instantiated in the copied "Tom:A".
- If "Copy subcells" is not checked, the instance in the new "Tom:A" points to the old "Frank:B".
- If "Copy subcells" is not checked and "Use existing subcells" is checked, the instance in the new "Tom:A" points to the existing cell "Tom:B". In order for this to work, however, the size and exports of "Tom:B" must match the original in "Frank:B".

Therefore, if "Copy subcells" is checked, "Use existing subcells" is implied.