The + syntax should be used in preference to the obsolete ? form.

The + prefix is a versatile condition field syntax which may be used with integer parameters (see Numerical conditions) or with strings. A string condition may be applied to a pre-defined symbols (see Special fields in composed strings) as well as User-defined fields. Full nesting is supported, so the 'found' and 'not_found' parameters may themselves consist of another field expression or conditional field, provided that they resolve to a string.

Click to expand/collapse this hidden text{+fieldname=['found'],['not_found']}
The string value of this composite field depends on whether a field is found or not.

found

This is a string and must be enclosed within a pair of quote characters. It is the value that the composite field returns if fieldname is found.

not_found

This string, in quotes, is the value that the composite field returns if fieldname is not found.

See also Examples: Composite fields

Obsolete syntax:

Click to expand/collapse this hidden text{?fieldname=['true_value'][,'false_value']}
This expression determines whether or not a field value is present in a data-field: superseded by +fieldname syntax above.

?fieldname=

Must start with a question mark followed by a field name and an equals sign.

true_value

(optional)

The value assigned if a value exists for the named field. If true_value is a single 'word', it need not be in quotes.
Default value is T  if true_value parameter value is omitted from the expression.

false_value

(optional)

The value assigned if a value for the named field does not exist. If false_value is a single 'word' quotes may be omitted.
Default value is F  if false_value parameter value is omitted from the expression.

See also {?fieldname} below.
•{?fieldname}
To just return the default values T if the field value exists or F if it doesn't, it is sufficient simply to precede the field name by a question mark. Use +fieldname syntax instead.

See also More on defining composite fields.

Links

Numerical conditions

Examples|Composite fields