Tail probability, strictly between 0 and 0.5.
The median is carried separately on BoxenPoint and is not a rung, so
0.5 is out of range rather than a way of naming it: a rung at 0.5
would put two positions labelled 50th percentile either side of the one
already called median. Values outside the range are dropped.
The lower quantile of the pair: the p quantile.
The upper quantile of the pair: the 1 - p quantile.
One rung of a letter-value ladder: a pair of quantiles symmetric about the median.
pis the tail probability, which is how letter-value plots are defined and how the libraries that draw them report it:p = 0.25is the rung spanning the middle half,p = 0.125the middle three quarters, and so on inwards from the median. The trace converts it to percentiles for the announcement, because "the 12.5th percentile" is a number a reader can place and "p is 0.125" is one they have to convert.