Need to provide an ability to select several blocks with keyboard and by mouse from center of block.

By mouse

• By mouse moving from block's text and over next block, select these two blocks
• By mouse moving from block's text and over previous block, select these two blocks

By keyboard selection

• By SHIFT+DOWN at last line, select current and next blocks.
• By SHIFT+UP at the first line, select current and previous block
• By second СMD+SHIFT+DOWN in any line, select current and next blocks.
• By second СMD+SHIFT+UP in any line, select current and previous blocks.

Select more blocks

• If one or more blocks are selected, by SHIFT+DOWN, select one more block below
• If one or more blocks are selected, by SHIFT+UP, select one more block above

Deselect blocks

• If 1+ blocks was selected by shift+up, by next SHIFT+DOWN deselect one upper block
• If 1+ blocks was selected by shift+down, by next SHIFT+UP deselect one lowest block

Related issues
#702
#672