Labeled USINGs and qualified symbols

The format of the assembler USING instruction now lets you code a symbol in the name entry of the instruction. When a valid ordinary symbol, or a variable symbol that has been assigned a valid ordinary symbol, is specified in the name entry of a USING instruction, it is known as the USING label, and the USING is known as a labeled USING.

Labeled USINGs provide you with enhanced control over the resolution of symbolic expressions into base-displacement form with specific base registers. The assembler uses a labeled USING when you qualify a symbol with the USING label. You qualify a symbol by prefixing the symbol with the label on the USING followed by a period.