JavaScript verify text inputs as the user types

gistfile1.js

// used to verify characters and prevent incorrect input as the user is typing.
// TODO: detect special characters like period/comma/?/etc. in the first regexp
// USAGE: use the keydown event: "return dynamicVerify(e, '[0-9a-zA-Z]');"
// e = event, re = regexp for allowed characters, ce = regexp for allowed key codes
function dynamicVerify(e, re, ke) {
    var key = e.keyCode || e.which;
    var keychar = String.fromCharCode(key);

    var rexp = new RegExp(re);
    var kexp = new RegExp(ke);                                                                                                                                                                                                                                                  

    // differentiate lower/upper case
    if (!e.shiftKey) {
        keychar = keychar.toLowerCase();
    }

    // allow capital letters if they match rexp
    if (e.shiftKey && rexp.test(keychar) === true && key >= 65 && key <= 90) {
        return true;
    }
    // otherwise only allow shift tab
    else if (e.shiftKey && key != 9) {
        return false;
    }

    // allow specific key codes using kexp
    if (ke && ke != '') {
        if (kexp.test(key) === true) {
            return true;
        }
    }

    // ctrl/command-a/x/c/v (select all/cut/copy/paste)
    if ((e.ctrlKey || e.metaKey) && (key == 65 || key == 88 || key == 67 || key == 86)) {
        return true;
    }

    // allow backspace, left/right arrow, etc.
    if (key < 48 || (key > 90 && key < 186)) {
        return true;
    }

    // allow specific characters using regexp
    if (rexp.test(keychar) === true) {
        return true;
    }

    // no matches
    return false;
}