regex - A specifc Regular expression in XSLT -

my doubt specific:

whats meaning of regex in xslt:

"replace(concat('1-',replace($contentsep[1],'\.','-')),'-0(\d+)','-$1')"

my '$contentsep[1]' like: '01.01.01'.

my main doubt in meaning of '-0(\d+)' , '-$1'.

replace($contentsep[1],'\.','-') makes input: 01-01-01

concat('1-', ...) makes transformed input: 1-01-01-01

finally replace('...', '-0(\d+)','-$1') making transformed input : 1-1-1-1. removing 0 before number(\d).

And