a Doncian channel is simply a channel that represents the highest high and lowest low of the price for a certain period (number of bars) -- the concept of watching these extreme values is the basis of many other technical indicators in chart analysis.
A script like this may come useful for setting entry and exit levels and can be used to plot the DC & Fib levels for a higher resolution than the chart - in the example, we're looking at the DC & its Fib levels for the on a 30-min chart.
there are 3 adjustable levels that are set by default to 0.368, 0.618, and 1.272 -- and they can be set to any other levels we need to monitor - not necessarily Fib-based at all - say to determine a possible breakout or breakdown... etc
this script makes use of the "resolution" and "inline / group" features (powers) of Pine :)
In true TradingView spirit, the author of this script has published it open-source, so traders can understand and verify it. Cheers to the author! You may use it for free, but reuse of this code in a publication is governed by House Rules. You can favorite it to use it on a chart.