Examples that Angle should parse but doesn't

I have several examples of Angle failing to parse where it should:

    from astropy.coordinates import Angle, ICRSCoordinates
    import astropy.units as u

    a1 = Angle('10"') # 10 arcseconds
    a2 = Angle("10arcsec") # AttributeError: 'str' object has no attribute 'to'
    a3 = Angle("10 arcsec") # AttributeError: 'str' object has no attribute 'to'
    a4 = Angle(10, unit=u.arcsec) # bounds error