I'd like to draw a vertical dashed line at every first bar of a month (for daily and weekly charts) or a year (for monthly charts). How can I do that? I don't know how to get those bar indexes.
Addition: I read in this post that "line.new" has a restriction to 54 lines max per indicator. But when using the plot function in histogram style (=plot only single vertical histogram bars), I cannot plot dashed lines... and I prefer a solution with dashed lines...