BtrvInsert adds a new record to the data file. The data is passed in the
array DataVar. If key fields are used, or if you are using traditional
style fixed-length fields, then the first elements of the array must
match the data structure of the file you defined with BtrvCreate. All
elements of the array after these fields are written to the
variable-length part of the file. The variable-length part can contain
MarxMenu multi-dimensional data structures.