[sheetjs]

Software Arts published an official technical specification of the DIF file format in 1983. [1] (to save a file in the DIF format, /S#S in VC)

It is certainly an interesting format, and Excel completely mangles the data (whether it was intentional is up for debate). For example, the value

    1,0
    "0.3"

represents the literal string 0.3 in VisiCalc (the 1,0 indicates that the next line is a string). Excel ignores the typing and tries to parse as a value, interpreting it as the number 0.3. Like with CSV, there's an awkward formula workaround for generating a file with the text "0.3":

    1,0
    "=""0.3"""

 [1] https://atariwiki.org/wiki/attach/VisiCalc/DIF_Technical_Specification.pdf