Fractal repaints?! Doesn't always - but why does fractal
indicator, built in to MT4(build 1090), repaint? Should it?
I know for example custom fractal indicators don't repaint
Fractals are a lagging Indicator and yes, it can repaint but only within the last three bars (including the current one).
It is normal to see repaints of the most recent fractal within this 3 bar region, because its right-hand shoulder has still not completed 2 bars at least, due to the definition that a complete fractal must be 5 bars at least (a middle bar, and two bars on each shoulder).
The indicator will show a tentative fractal developing while it still has less then two complete bars on its right-hand side. After that, it then becomes stable.
If using the iFractal() function, it is only safe to look for complete fractals from bar-shift  onward. At bar-shift , the fractal will be incomplete and will only confirm when it shifts to position .
For all other bar-shifts, the fractals are confirmed and do not repaint. Repainting, is therefore only visible within the most recent three bars (including the current one, which will never have a fractal on it).
The article - Construction of Fractal Lines
Fractals are used by practically all traders. However, if you ask them what a fractal is, they will at best answer that it is an indicator in the Bill Williams' system. The more advanced traders will say that it is a sequence of 5 bars where, if the middle bar's High is higher than those of other bars in the sequence, it is an Up fractal and, if the middle bar's Low is lower than those of other bars, it is a Down fractal. As the phrase goes, "This is all I can tell about the war”.
A brief description of fractals, particularly of their nature and use, is given in the Bill Williams' book named New Trading Dimensions: How to Profit from Chaos in Stocks, Bonds, and Commodities.
Forum on trading, automated trading systems and testing trading strategies
Sergey Golubev, 2008.09.08 17:31
The forum threads (indicators, trading systems and the EAs)
And the last information which I found using search:
Sergey Golubev, 2017.10.29 07:28
How To Trade - Fractal Indicator and How Does It Work (based on blog post)
The fractals are technical indicators, part of the Bill Williams’ indicators. Unlike any other indicators, this one is not a line or histogram bars; it is just a simple arrow on top of or below the bars of the price chart. These fractals are formed when five consecutive bars align in a strict manner. There are two types of fractals:
Bearish fractals: this fractal forms over a bar in the price chart, only if the high of this bar is higher than the high of the previous two and next two bars. In real-life trading this fractal indicates a possible bearish movement.
Bullish fractals: this fractal forms below a bar in the price chart, if the low of this bar is lower than the low of the previous two and next two bars. When you see this fractal, you should expect a bullish movement.
It is important to mention that the Bill Williams’ fractals are illustrated a bit late on the chart, because you need the fifth bar to close, in order to determine the highest high or lowest low. The fractals are trading signals, but they are far too insufficient to count on them alone: the buy fractal indicates a possible buy order and vice versa.
The fractals point out the strong levels. You can easily draw a line to connect multiple fractals to form either a resistance or a support line. These levels work exactly the same as the trend lines. If you take a look at the image, you will see the resistance line and the buy signal. We get this signal, because the price breaks the strong resistance level. However, if you take a close look at the chart before this moment, you will see a couple of sell signals. This clearly points out how inconclusive are the fractals alone.
If you have paid attention on the Trend Lines page, you already know that some traders use the fractals to build their trend line. We really like this strategy, but it is not something revolutionary.
Bill Williams’ fractals and Alligator indicator. These two indicators share great synergy and we will take a quick glance in the image. It is the same as the previous, but we have added the Alligator and this changes the picture quite a lot. Take a look at the buy signal; do you see now why we have not opened a sell order before the buy signal? The price moved above the Alligator and we needed to see a breach of the indicator’s levels and a couple of sell fractals, but did not see that. Instead, the price kept on moving above the Alligator and it even broke the resistance level, which gave us a clear idea of the future movement – buy and take profit.
Fractals in CodeBase - search link.