cmd = see description start-column = ? start-row = 1 first-row = ? last-row = ? [See also scroll down which shares this code and is distinguished by having only one parameter and having the first parameter != 0]
This sequence is used with mouse highlight mode to communicate the selection start and allowed rows.
If cmd is 0 then the highlighting is aborted and the terminal uses non highlighting mouse handling as in mouse down+up tracking.
If cmd is non-zero then start-column and start-row specify the selection start and first-row specifies the first allowed row for the selection and last-row specifies the first row that the selection may not enter into.