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.
study("IB Bars", overlay=true) //Inside Bars insideBar() => high <= high and low >= low ? 1 : 0 plotshape(insideBar(), style=shape.flag, color=blue)