The URL (web address) shown by your browser starts with https because you visit this site using a secured connection. Note that the URI reference (identifier) of FLANGED CONNECTION (dexpi) to be used in DEXPI-compliant Proteus files starts with http - as shown below:
Flange connections are used preferably for above-ground pipes, for example in pumping stations, waterworks, pipe basements or upright tanks, but also in underground piping in the area of pipe junctions and intersections.
"Flange connections are used preferably for above-ground pipes, for example in pumping stations, waterworks, pipe basements or upright tanks, but also in underground piping in the area of pipe junctions and intersections."