Filter using url QueryString parameter 'a=…' does not always work for all fields

Question

On a SharePoint SearchResults page the core results webpart can be refined or filtered using the QueryString paramters 'r=' or 'a=' in the url. I am attempting to use the 'a=' parameter which works great for the fields 'format' and 'author' but I have no been able to get it to filter on Modified Date aka 'write' or on Site Url aka 'sitename'

Example:

 //queryString was "r=write%3D%22AQlQYXN0IFllYXIFd3JpdGUAFwFbMjAxMy0wNC0xMFQwMDowMDowMFo7XQ%3D%3D%22"
 //removing the urlEncoding %3D%22 you are left with the below value.
r="AQlQYXN0IFllYXIFd3JpdGUAFwFbMjAxMy0wNC0xMFQwMDowMDowMFo7XQ";

/*following decode written by http://stackoverflow.com/users/516910/broc-seib */
decodeBase64 = function(s) {
    var e={},i,b=0,c,x,l=0,a,r='',w=String.fromCharCode,L=s.length;
    var A="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
    for(i=0;i<64;i++){e[A.charAt(i)]=i;}
    for(x=0;x<L;x++){
        c=e[s.charAt(x)];b=(b<<6)+c;l+=6;
        while(l>=8){((a=(b>>>(l-=8))&0xff)||(x<(L-2)))&&(r+=w(a));}
    }
    return r;
};
s2=decodeBase64(r);
alert(s2);

If you run the code above in your browser you will see the search was 'Past Year | write'. and it returned a few hundred results. How do I get this query to work using the 'a=' paramter ?

Answer 1

There was two issues, first I was always using the query format field="value" but that only matches exact values unlike field:"value", also depending the datatype not all values use quotes. Another issue is CustomFilters which mask the original value such as Past Year instead of passing -365..

For more on this visit the MSDN page which explains the syntax