be explicit that the string is empty rather than possibly missing
disallow encrypted export for BK4 (they're not encrypted), removes type
check
simplify replaceall in showdownset (don't call ReplaceAll 4x, just get
valid chars and rebuild)
simplify get ribbon sprite name (precompute ToLower and appended values
showdownset: contains char instead of string
gameinfo: static readonly array instead of redefining new on update
legality: order of operation / value reuse / simplification / comments
pkx: compare char instead of single character string
header/footer: move assignment into method as an out instead of ref
