4.3: Line lengths
PGN data are organized as simple text lines without any special bytes or markers for secondary record structure imposed by specific operating systems. Import format PGN text lines are limited to having a maximum of 255 characters per line including the newline character. Lines with 80 or more printing characters are strongly discouraged because of the difficulties experienced by common text editors with long lines.
In some cases, very long tag values will require 80 or more columns, but these are relatively rare. An example of this is the "FEN" tag pair; it may have a long tag value, but this particular tag pair is only used to represent a game that doesn't start from the usual initial position.