Below is the code from extjs 4.1 RC3 api.
Looking at validIdRe, you guys are disallowing id start with number. Is there any reason for this?

{
xtype:"panel",
id:"099890-333"
}


Code:
 escapeId: (function()
{
        var validIdRe = /^[a-zA-Z_][a-zA-Z0-9_\-]*$/i,
            escapeRx = /([\W]{1})/g,
            escapeFn = function(match, capture){
                return "\\" + capture;
            };

        return function(id) {
            return validIdRe.test(id)
                ? id
                : id.replace(escapeRx, escapeFn);
        };
    }())