E1EVMCST02 is a standard SAP Structure which is used to define the field attributes of IDoc segment E1EVMCST02. The segment is used within the below IDoc to send Detail (or 'Confirmation') Status information via the IDoc send process
Below is the standard documentation available and a few details of the fields which make up this IDoc segment structure. To view further details checkout the IDoc links above or use relevant transactions such as WE30(IDoc development), WE31 (segment development)...Also check here for more IDoc related development help, or you can obviously also use standard dictionary object dev tcodes such as SE11, SE80 etc...