Autonomy can therefore be viewed as the oil that enables the wheels of XML to turn in practice. The limitations of XML begin with the manual process employed to choose and apply the tags. One example of the effect of human behaviour and the inherent limitations of manually describing information albeit from existing descriptions -is illustrated by the results of a US Department of Defense edict, mandating that internal users responsible for authoring documents also create an appropriate description of the document's content. At first glance, a seemingly sensible and pragmatic decision. An individual's ability to describe information is dependant upon their personal experience, knowledge and opinions.
Further complications arise when subjects incorporate multiple themes.
The decision process is both complex and time consuming and introduces yet more inconsistency, particularly when the sheer number of options available to a user is considered. For example, over 800 tags for general newspaper subjects make the task of choosing a potentially basic subject description in a reasonable time-scale, an even more challenging process. Idea Distancing Tags also fail to highlight the relationships between subjects. The first category may contain information about the way the wings are designed to achieve low air resistance. The latter category discusses ways in which efficient aerofoils are made.