This was a formulation that differed from the standard inflation-targeting framework of the time, which was typically based around a point target for inflation. But there were sound reasons why this definition was put in place.
In common with central banks across the world, the ECB faced a macroeconomic environment before the crisis that was predominantly defined by low volatility and moderate shocks, with the distribution of shocks to inflation almost exclusively to the upside. In the euro area, HICP energy prices rose by 80% between January 1999 and September 2008.