Another topic that was raised is the depiction of a quote (') character in an Assembler DC statement. This statement defines a "normal" character string -
STRING1 DC C'HELLO WORLD'
The HELLO WORLD is the text; it is delimited by a single quote character. Now what do you do if you need a quote character in the string? The 48 or 60 bit character definition in early System/360, much less its BCD based ancestors did not have the double quote ("). The convention was to use two consecutive single quote characters to define a single quote character in the assembled string -
STRING2 DC C'''HELLO WORLD'''
to generate 'HELLO WORLD'. The first triple ' defines the start of the character string followed by a single ' in the text. The second triple ' defines another single quote in the string and the end of the string. This convention was followed for other special characters, notably the & character.
This convention was followed through in other contexts like JCL :
// EXEC PGM=XYZ,PARM='HELLO WORLD'
// EXEC PGM=XYZ,PARM='''HELLO WORLD'''