Hi Spin,
I think they refer to this (see attached image). There is an open-source indicator on TradingView that display unfilled gaps (see attached code). I do not necessarily trade them (unless it is an additional context to my strategy), but some traders trade them often as we all know that most gaps are filled at some point.
If you would like to code and put it up for sale on your site, I would also add the following information to the cursor data window, which will allow users to create alerts based on these conditions:
- Gap type: 1.0 (for a bullish gap) or -1.0 (for a bearish gap)
- Bar Index of the gap: (for example, (bar number == 10), meaning that the most recent bullish gap took place 10 bars ago from the current bar, and it is still not invalidated. This number will increase as time flies) (I would display this on the current bar, so it would be easy to track the most recent unfilled gap)
- Top price of the gap: ..... (price)
- Bottom price of the gap: ..... (price)
- Midpoint of the gap: ..... (price)
- Invalidation: (You could also add the Wick/Close invalidation, or 25%, 50%, 75% invalidation levels, similar to what you mentioned above).
- A new gap happened: ..... (true or 1.0) (see attached code)
- A gap was closed: ..... (true or 1.0) (see attached code)