HP Fortran Programmer's Reference (September 2007)

Language elements
Statement labels
Chapter 2 45
Statement labels
A Fortran 90 statement may have a preceding label, composed of one to five digits. All
statement labels in the same scoping unit must be unique; leading zeroes are not significant.
Although most statements can be labeled, not all statements can be branched to.
The FORMAT statement must have a label. The INCLUDE line, which is not a statement but a
compiler directive, must not have a label.