 right|frame|b is transcluded in the document a. in computer science, transclusion is the inclusion of a document or part of a document into another document by reference. for example, an article about a country might include a chart or a paragraph describing that country's agricultural exports from a different article about agriculture. rather than copying the included data and storing it in two places, a transclusion embodies modular design, by allowing it to be stored only once (and perhaps corrected and updated if the link type supported that) and viewed in different contexts. the reference also serves to link both articles. transclusion is usually performed on demand at the time one document referencing another is opened, and is normally automatic and transparent to the end user. the result appears to be a single integrated document, even though its parts were assembled on-the-fly from several separate documents which may have come from different computers located in different places. the term was coined by hypertext pioneer ted nelson in 1963. == technical considerations == === context neutrality === transclusion works better when transcluded sections of text are self-contained, so that the meaning and validity of the text is independent of the context in which it appears. for example, formulations like "as explained in the previous section" are problematic, because the transcluded section may appear in a different context, causing confusion. what constitutes "context neutral" text varies, but often includes things like company information or boilerplate. === parameterization === under some circumstances, and in some technical contexts, transcluded sections of text may not require strict adherence to the "context neutrality" principle, because the transcluded sections are capable of parameterization. parameterization implies the ability to modify certain portions or subsections of a transcluded text depending on exogenous variables that can be changed independently. this is customarily done by supplying a transcluded text with one or more substitution placeholders. these placeholders are then replaced with the corresponding variable values prior to rendering the final transcluded output in context. ==history and implementation by project xanadu== ted nelson (who had also originated the words "hypertext" and "hypermedia") coined the term "transclusion" in his 1982 book, literary machines. part of his proposal was the idea that micropayments could be automatically exacted from the reader for all the text, no matter how many snippets of content are taken from various places. however, according to nelson, the concept of transclusion had already formed part of his 1965 descriptiontheodor h. nelson, "a file structure for the co
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