The enclosing quotation marks or apostrophes are not part of the value. If an unrecognized keyword is present, any program reading a DIF file should ignore the line or group introduced by that keyword. It is a local option whether to issue a warning message. However, the textline must be parsed to be sure to find and ignore any continuation. Field labels begin at the first non-blank character on a line.
Acronyms can be in all capital letters.
The complete file should be human readable exactly as delivered. Use ragged right margins, no right justification. A minimum longitude always means that which is furthest west. A maximum longitude always means that which is furthest east. A minimum latitude is always that which is furthest south.