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                                            STEP file format is defined by ISO 10303-21 Clear Text Encoding of the Exchange
                                            Structure. There are three editions of ISO 10303-21. First edition was released
                                            in 1994 and last was released in 2016. In last edition added is anchor, reference
                                            and signature sections to support external references, support for compressed exchange
                                            structures in an archive, digital signatures and UTF-8 character encoding.
                                         
                                        
                                            ISO 10303-21 structure it contains two sections, header and data section. Header
                                            section has fixed structure consisting 3 to 6 groups in given order. The DATA
                                            section contains application data according to one specific express schema encoded
                                            following some simple principles. 
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