in children. Whilst birth registration alone does not confer citizenship on a child, the documentation of place of birth and parentage is instrumental in proving the link between an individual and a state for the acquisition of nationality. The United Nations Children's Fund (UNICEF) estimated in 2013 that 230 million children under the age of 5 have not been registered. Not holding proof of nationality—being "undocumented"—is not the same as being stateless, but the lack of identity documents such as a birth certificate can lead to statelessness. Millions of people live, or have lived, their entire lives with no documents, without their nationality ever being questioned. Two factors are of particular importance: whether the nationality in question was acquired automatically or through some form of registration whether the person has ever been denied documents on the basis that they are not a national. If nationality is acquired automatically, the person is a national regardless of documentation status (although in practice, the person may face problems accessing certain rights and services because they are undocumented, not because they are stateless). If registration is required, then the person is not a national until that process has been completed. As a practical matter, the longer a person is undocumented, the greater the likelihood that they will end up in a situation where no state recognizes them as a national. Renunciation In rare cases, individuals may become stateless upon renouncing their citizenship (e.g., "world citizen" Garry Davis and, from 1896 to 1901, Albert Einstein, who, in January 1896, at the age of 16, was released from his Württemberg citizenship after, with his father's help, filing a petition to that effect; in February 1901 his application for Swiss citizenship was accepted). People who subscribe to Voluntaryist, Agorist, or some other philosophical, political, or religious beliefs may desire or seek statelessness. Many states do not allow citizens to renounce their nationality unless they acquire another. However, consular officials are unlikely to be familiar with the citizenship laws of all countries, so there may still be situations where renunciation leads to effective statelessness. Non-state territories Only states can have nationals, and people of non-state territories may be stateless. This includes for instance residents of occupied territories where statehood never emerged in the first place, has ceased to exist and/or is largely unrecognized. Examples include the Palestinian territories, Western Sahara and Northern Cyprus (depending on the interpretation of