The area between the basic trendline and the parallel line is known as a trend channel. Such channels seem to appear more often in large cap companies (actively traded stocks which are widely held and have large public participation) and rather infrequent in thinly held stocks.
Once a trend channel is clearly identified, any failure of a rally to reach the top line or parallel is taken as a sign of weakness in the trend (this is not a benchmark rule but would needs to be ratified on a case to case basis).
Similarly, the strength of a channel can be identified when a reaction from a parallel line fails to carry prices back to the basic trendline but bottoms out somewhere above it.
The stiffness (angle of the ascent) of a channel is a relative term and cannot be easily quantified. The slant/angle of the channel would vary according to the various cycles and waves, but would finally become more steep at an advanced stage in the bull market.
A decisive breach of a trend channel needs to carefully identified as there could also be a false move. A sideways consolidation might result in a breach but a valid breach will signal a probable change in the underlying trend and also make a tremendous difference it terms of a profit or loss.
The test for validity for the breach depends on the extent of the breach - that is, the stock price should have fallen approximately 3 per cent below the basic trendline and volumes would tend to heighten starting at a 2 per cent price decline from the basic trendline.