Label Field

The first field on the source line is the label field. The label field follows these rules:

• A space or tab as the first character indicates that there is no label for this line.
• An alphabetic character as the first character indicates that the line contains a symbol called label.
• An underscore character as the first character indicates that the label is a local label.

A label may be indented (not starting with the first character of the line) if the last character in the label is a colon (:). Local labels have a scope limited by any two bounding non-local labels. Local labels are useful in the instance that a label is needed, but you don't need to refer to it outside of a limited scope, such as in the case of a DO loop.

You may not define a label twice, unless you do so in conjunction with a SECTION, a SET directive, or as a local label.