All DASDL source input is free format. Statements can appear in columns 1 through 72 and can be continued from one input record to another. Each input statement is terminated by a semicolon (;).

DASDL source input can contain a sequence number in columns 73 through 80. Normally 8‑digit numeric values are used, but any combination of characters is allowed. All blanks in the sequence number field represents the lowest sequence number. When both CARD and TAPE files are used as input, DASDL uses the sequence numbers to merge the source images. If the SEQERR option is set, an error message is given whenever an input sequence error is encountered.