Want to know the meaning of ""/^\s+|\s+$/g" in xsl

Hi,
Can someone tell me what does the below string does? the first parameter to the replace function looks like its a regex but have no idea what it does.. can someone help me decipher it!!
This was found in a xsl file and in a function which performs the trimming of a given string.

I am very much keen to know the meaning of "/^\s+|\s+$/g"

Thanks in advance

function stringTrim(instring)
{
    var outstring = instring;
    return outstring.replace(/^\s+|\s+$/g,"");
}

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