## The New Font Selection Scheme

http://makingtexwork.sourceforge.net/mtw/ch05.html

The New Font Selection Scheme is a method for selecting fonts in Plain TeX and LaTeX.

The NFSS defines a method of font selection used in place of TeX's primitive \font command. The problem with font selection using \font is that it ties a control sequence to a particular font at a particular size, which has unpleasant consequences when more than one font is used in a document. Consider the definition \font\it=cmti10. This associates the control sequence \it with the italic Computer Modern font (at 10pt)… (which is might) not what you wanted. The NFSS overcomes this difficulty by describing each font with five independent parameters: encoding, family, series, shape, and size.

Font encoding
The encoding parameter identifies the encoding vector of the font. Encoding vectors play an important role in the selection of characters in a font. Encoding vectors are described more thoroughly later in this chapter. TeX Text, TeX Math Italic, and Adobe Standard are all encoding vectors.
Font family
The family parameter describes the typeface of the font. Computer Modern, Times Roman, Helvetica, Galliard, and Gill Sans are all families.
Font series
Font series describes the joint notions of weight and width. Weight is a measure of how darkly each character is printed, and width is a measure of how wide or narrow the font is. Standard abbreviations for weight and width are shown in Table Table 5.1. Normal, bold-compressed, extrabold-ultraexpanded, and light-medium are all examples of font series
Font shape
The shape, in conjunction with series, defines the appearance of the font. Shape generally refers to the style of the face. Bold, italic, slanted, and outline are all examples of font shape.
Font size

Font size defines both the size of the characters and the spacing between lines of text in that size. The distinction between design size and magnification, discussed at length in the first part of this chapter, is hidden within the NFSS; you need only select the size you want.[59]

The spacing between lines of text is described as the (vertical) distance between the baselines of two consecutive lines of type. It is usually about 20\% larger than the size of the font. For example, a 10pt font is usually printed with 12pts between the baselines of consecutive lines. The inter-line distance that looks best depends on the font and other design elements of the document. There really isn't a good rule for the value that looks best, which is why you have to specify it.