subwords includes all the subwords of length 1 (., e, n, c, y, etc.), of length 2 (.e, en, nc, etc.), etc., up to the subword of length 14, which is the word itself, including the markers. TeX will then look into its list of hyphenation patterns, and find subwords for which it has calculated the desirability of hyphenation at each position. In the case of our word, 11 such patterns can be matched, namely 1c4l4, 1cy, 1d4i3a, 4edi, e3dia, 2i1a, ope5d, 2p2ed, 3pedi, pedia4, y1c. For each position in the word, TeX will calculate the maximum value obtained among all matching patterns, yielding en1cy1c4l4o3p4e5d4i3a4. Finally, the acceptable positions are those indicated by an odd number, yielding the acceptable hyphenations en-cy-clo-pe-di-a. This system based on subwords allows the definition of very general patterns (such as 2i1a), with low indicative numbers (either odd or even), which can then be superseded by more specific patterns (such as 1d4i3a) if necessary. These patterns find about 90% of the hyphens in the original dictionary; more importantly, they do not insert any spurious hyphen. In addition, a list of exceptions (words for which the patterns do not predict the correct hyphenation) are included with the Plain TeX format; additional ones can be specified by the user. Metafont Metafont, not strictly part of TeX, is a font description system which allows the designer to describe characters algorithmically. It uses Bézier curves in a fairly standard way to generate the actual characters to be displayed, but Knuth devotes substantial attention to the rasterizing problem on bitmapped displays. Another thesis, by John Hobby, further explores this problem of digitizing "brush trajectories". This term derives from the fact that Metafont describes characters as having been drawn by abstract brushes (and erasers). It is commonly believed that TeX is based on bitmap fonts but, in fact, these programs "know" nothing about the fonts that they are using other than their dimensions. It is the responsibility of the device driver to appropriately handle fonts of other types, including PostScript Type 1 and TrueType. Computer Modern (commonly known as "the TeX font") is freely available in Type 1 format, as are the AMS math fonts. Users of TeX systems that output directly to PDF, such as pdfTeX, XeTeX, or LuaTeX, generally never use Metafont output at all. Macro language TeX documents are written and programmed using an unusual macro language. Broadly speaking,