The same visual layout may be used to display disparate concepts. Encoding instances of such ambiguous notation by using well-designed markup abstracts out the layout details from the document encoding, and allows an information agent to identify the different concepts correctly. We illustrate this with a concrete La)TeX example.
The visual layout of stacking one mathematical object above another, separated by a horizontal line (horizontal rule), could be used in several contexts.
\frac{object-1}{object-2} in both
cases makes it impossible to
disambiguate between the different interpretations. When
the same layout is used to denote different concepts,
these should be marked up distinctly.
For instance, in LaTeX, the author could extend the markup language by defining two new macros:
\def{\fraction}[2]{\frac{#1}{#2}}.
\def{\inference}[2]{\frac{#1}{#2}}.
Though stated in terms of La)TeX, the above requirement can be generalized to any encoding system. It merely states that objects that are semantically distinct but share a common visual representation should have distinct electronic encodings. This is essential in ensuring that such objects can be presented in other modalities, where they may not necessarily share the same displayed representation. More generally, such distinct encodings are also essential if we are to compute on the content encapsulated by the encoding.