Tweaked glossary entry for shaping engine.

src/content/docs/reference/glossary.md

@@ -296,7 +296,7 @@ Term | Definition
 <a id=''></a>SLDR|see <a href='#sldr'>SIL Locale Data repository</a>.
 <a id='smartfont'></a>smart font|a <a href='#font'>font</a> capable of performing transformations on complex patterns of <a href='#glyph'>glyphs</a>, above and beyond the simple character-to-glyph mapping that is a basic function of font rendering (see <a href='#cmap'>cmap</a>). The information specifying the smart behavior is typically in the form of extra tables embedded in the font, and will generally allow layered transformations involving one-to-many, many-to-one, and many-to-many mappings of glyphs.
 <a id='shaping'></a>shaping|the process of chosing the correct form or shape of characters in order to produce correct rendering.
-<a id='shapingEngine'></a>shaping engine|a software component, often built into an operating system, that provides text layout and smart font processing. Examples include [Harfbuzz](#harfbuzz), [DirectWrite](#directwrite), [CoreText](#coretext), [Universal Shaping Engine](#use).
+<a id='shapingEngine'></a>shaping engine|a software component that uses knowledge about script behavior to select the correct shapes of characters. Examples include [Harfbuzz](#harfbuzz), [DirectWrite](#directwrite), [CoreText](#coretext), and the [Universal Shaping Engine](#use). The [OpenType](#opentype) smart font system depends on an external shaping engine to provide knowledge of the appropriate shapes of characters, while the [Graphite](#graphite) and [AAT](#aat) systems include their own internal equivalent of a shaping engine.
 <a id='smartRendering'></a>smart rendering|a <a href='#render'>rendering</a> process that uses a <a href='#smartfont'>smart font</a>.
 <a id='sortkey'></a>sort key|a sequence of numbers that when appropriately processed using a particular standard algorithm will position the corresponding string in the correct sort position in relation to other strings. The sort key need not correspond one number to one <a href='#codepoint'>codepoint</a> in the input string.
 <a id='sfm'></a>Standard Format Marker (SFM)|an element of a proprietary format developed by SIL International and used by some linguistic software applications. A standard format marker begins with a backslash (\\); for example, `\p` would represent a paragraph tag. It is possible (and even probable) that SFMs in a single document have different character encodings. When converting to one encoding (Unicode) these must be converted with different mapping files.