src/PEAR/Config.php
function isDefined($key)
    {
        foreach ($this->layers as $layer) {
            if (isset($this->configuration[$layer][$key])) {
                return true;
            }
        }

        return false;
    }
function isDefined($key)
    {
        foreach ($this->layers as $layer) {
            if (isset($this->configuration[$layer][$key])) {
                return true;
            }
        }

        return false;
    }
Tells whether a given key exists as a config value.

@param string config key
@return bool whether <config key> exists in this object

@access public