/dist:    # match 'dist:'
     .*?      # match anything (including newlines), but only until the next part of the pattern starts to match
     (\d+)    # match 1 or more digits, and put these into $1
     .*?      # same as before
     km;      # match 'km;' (not needed unless you want to match a number of these in one string)
    /s        # treat the whole line as a single string