The Header Blocks contains global directives. This must be followed by at least one Source Block, which specifies an input source.
|GDSII||.gds, .str, .strm, .stream|
Only these extensions are recognized, however CGX and GDSII allow an additional .gz which will imply compression.
Basic defaults for the various output formats are as specified in the Export Control panel from the Convert Menu, or from the corresponding variables.
If a TopCell is given, a corresponding cell definition will be created in the output file, and all cells specified in Placement Blocks (the ``placements'') will be instantiated in the new cell. Whether or not a TopCell is given, the placements will be streamed to the output file, meaning that the cell definitions needed to describe the cell and possibly its hierarchy will be added to the output file. With a TopCell given, the placements will be instantiated in the new top cell in output. Otherwise, there is no placement, and redundant Placement Blocks will be ignored. The output file can end up with multiple top-level cells, which may be desirable when creating a library.
The Header can also contain any of the Source Block or Placement Block directives below. These will be used as defaults in all blocks that follow, but can be overridden from within the blocks, or set, modified, or reset between Source Blocks.