Field expressions (also known as FEXs) are a way to select fields of a record.
A FEX is composed by a sequence of elements separated by commas:
ELEM_1,ELEM_2,...,ELEM_N
Each element makes a reference to one or more fields in a record identified by a given name and an optional subscript:
Field_Name[min-max]
min and max are zero-based indexes. It is possible to refer to a field occupying a given position. For example, consider the following record:
Name: Mr. Foo
Email: foo@foo.com
Email: foo@foo.org
Email: mr.foo@foo.org
We would select all the emails of the record with:
The first email with:
Email[0]
The third email with:
Email[2]
The second and the third email with:
Email[1-2]
And so on. Note that a selection is an ordered set not allowing duplicated values. Thus, the field expression:
Email[0],Name,Email
is equivalent to
Email[0],Name,Email[1-2]