What's the charactor ‘^' mean in the qmake file?

[Michael_BJFU]

Recently i read the source of qt creator. However I found a lot of doubtable codes. Have look at the codes below:

defineReplace(cleanPath) {
    win32:1 ~= s|\\\\|/|g
    contains(1, ^/.*):pfx = /
    else:pfx =
    segs = $$split(1, /)
    out =
    for(seg, segs) {
        equals(seg, ..):out = $$member(out, 0, -2)
        else:!equals(seg, .):out += $$seg
    }
    return($$join(out, /, $$pfx))
}

defineReplace(cleanPath) {
    win32:1 ~= s|\\\\|/|g
    contains(1, ^/.*):pfx = /
    else:pfx =
    segs = $$split(1, /)
    out =
    for(seg, segs) {
        equals(seg, ..):out = $$member(out, 0, -2)
        else:!equals(seg, .):out += $$seg
    }
    return($$join(out, /, $$pfx))
}

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What do the four backslashs mean? and also the '|g', '^' ? I can't find anything useful in the document.