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v – start visual mode, mark lines, then perform an operation (such as d-delete)
V – start linewise visual mode
Ctrl + v – start blockwise visual mode
o – move to the other end of marked area
O – move to other corner of block
aw – mark a word
ab – a block with ()
aB – a block with {}
ib – inner block with ()
iB – inner block with {}
Esc – exit visual mode