New syntax:
if (<condition>) { <command>; <command> <commands> <commands> } else { <commands> }
Old syntax:
if (<condition>) <command-line> [; else if (<condition>) ...; else ...]
This version of gnuplot supports block-structured if/else statements. If the keyword `if` or `else` is immediately followed by an opening "{", then conditional execution applies to all statements, possibly on multiple input lines, until a matching "}" terminates the block. If commands may be nested.
The old single-line if/else syntax is still supported, but can not be mixed with the new block-structured syntax. See if-old.