Find difference of words between 2 words ,with in div content using regex

Hi,
I wanted to count how many words lies between 2 words from the content of div using regex.For highlighting .
Like for Example imagine  the div content is:
Indian Railways (reporting mark IR / ??. ??) is an Indian state-owned enterprise, owned and operated by the Government of Indiathrough the Ministry of Railways. It is one of the world's largest railway networks comprising 115,000 km (71,000 ...