Charge carrier Charge carrier In physics, a charge carrier is a particle or quasiparticle that is free to move, carrying an electric charge, especially the particles that carry electric charges in electrical conductors. Examples are electrons, ions and holes. In a conducting medium, an electric field can exert force on these free particles, causing a net motion of the particles through the medium; this is what constitutes an electric current. In different conducting media, different particles serve to carry charge: It can be seen that in some conductors, such as ionic solutions and plasmas, there are both positive and negative charge carriers,
Unique Particle Attribution which disambiguates it by saying that when an element matches both an element particle and a wildcard, the element particle wins. However, the UPA constraint itself remains in version 1.1. Unique Particle Attribution The Unique Particle Attribution (UPA) rule is a mechanism to prevent ambiguity in W3C XML Schema version 1.0. Due to the UPA rule the XML schema fragment given below is prohibited: Given the XML instance fragment: it is ambiguous whether <x> should be associated with the element declaration (xsd:element name="x"), or the wildcard (xsd:any). This ambiguity violates the UPA rule and the corresponding XML schema therefore needs