In addition to the global metadata and specific variable metadata the header
must specify positions for each variable in a record. The column start position
of the first element of each variable in a record, together with the (constant for each element in a variable)
field width of each entry must be specified as part of each variable
description. These have syntax
column_start = nn
column_width = mm
where nn and mm are numbers and the first column position is
counted as zero.
Columns of data can be skipped in tabular files by omitting the corresponding variable description. The column_start and column_width are sufficient to locate variables that are required, and entries interspersed between specified variables in each record may be ignored.