Minecraft wiki entry for execute, associated text: Full syntax tree
/execute . . .
… align <axes> -> execute
… anchored <anchor> -> execute
… as <targets> -> execute
… at <targets> -> execute
… facing (<pos>|entity <targets> <anchor>) -> execute
… in <dimension> -> execute
… positioned (<pos>|as <targets>) -> execute
… rotated (<rot>|as <targets>) -> execute
… store (result|success) . . .
… block <targetPos> <path> <type> <scale> -> execute
… bossbar <id> (max|value) -> execute
… entity <target> <path> <type> <scale> -> execute
… score <targets> <objective> -> execute
… storage <target> <path> <type> <scale> -> execute
… (if|unless) . . .
… block <pos> <block> -> [execute]
… blocks <start> <end> <destination> (all|masked) -> [execute]
… data . . .
… block <sourcePos> <path> -> [execute]
… entity <source> <path> -> [execute]
… storage <source> <path> -> [execute]
… entity <entities> -> [execute]
… predicate <predicate> -> [execute]
… score <target> <targetObjective> . . .
… (<|<=|=|>|>=) <source> <sourceObjective> -> [execute]
… matches <range> -> [execute]
… run <command>
where -> execute represents the start of another subcommand.