  This empirical paper examines the adoption of PHP releases in the the
contemporary world wide web. Motivated by continuous software engineering
practices and software traceability improvements for release engineering, the
empirical analysis is based on big data collected by web crawling. According to
the empirical results based on discrete time-homogeneous Markov chain (DTMC)
analysis, (i)~adoption of PHP releases has been relatively uniform across the
domains observed, (ii) which tend to also adopt either old or new PHP releases
relatively infrequently. Although there are outliers, (iii) downgrading of PHP
releases is generally rare. To some extent, (iv) the results vary between the
recent history from 2016 to early 2017 and the long-run evolution in the 2010s.
In addition to these empirical results, the paper contributes to the software
evolution and release engineering research traditions by elaborating the
applied use of DTMCs for systematic empirical tracing of online software
deployments.
