<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def parseDockerAppliance(appliance):
 """ Takes string describing a docker image and returns the parsed registry, image reference, and tag for that image. Example: "quay.io/ucsc_cgl/toil:latest" Should return: "quay.io", "ucsc_cgl/toil", "latest" If a registry is not defined, the default is: "docker.io" If a tag is not defined, the default is: "latest" :param appliance: The full url of the docker image originally specified by the user (or the default). e.g. "quay.io/ucsc_cgl/toil:latest" :return: registryName, imageName, tag """

    appliance = appliance.lower()

    # get the tag
    if ':' in appliance:
        tag = appliance.split(':')[-1]
        appliance = appliance[:-(len(':' + tag))] # remove only the tag
    else:
        # default to 'latest' if no tag is specified
        tag = 'latest'

    # get the registry and image
    registryName = 'docker.io' # default if not specified
    imageName = appliance # will be true if not specified
    if '/' in appliance and '.' in appliance.split('/')[0]:
        registryName = appliance.split('/')[0]
        imageName = appliance[len(registryName):]
    registryName = registryName.strip('/')
    imageName = imageName.strip('/')

    return registryName, imageName, tag