The .incld directive includes the assembler statements in the file filename as part of the code being assembled.
The file must be a symbolic file; the default file extension is determined for the source file on the invocation line.
If the included lines are to be listed, the proper control line must be in the source code. See the .list directive.
More exactly, the .incld directive causes the assembler to read source code from the specified file until an end-of-file mark (or .end directive) is reached. Then it again starts reading source code from the assembly input file.
.incld directives may be nested 100 deep.
The directory search order is described in the Section called include file search order in Chapter 2.