Storing pairs of strings inside plone.app.registry
class IMyPair(Interface):
value = schema.TextLine(title=u"value", required=True)
title = schema.TextLine(title=u"title", required=False)

class MyPair(object):
    implements(IMyPair)
    def __init__(self, value='', title=''):
    self.value = value
    self.title = title

class IMyConfigPanel(Interface):

    entry = schema.List(
        title=_(u'Foo'),
        value_type=schema.Object(IMyPair, title=u"entry"),
        required=True
    )