19. The one or more non-transitory computer readable media of claim 14 , wherein the request for the network document includes a serial number and specifies a second set of glyphs, and wherein the computer readable instructions, when executed, further cause the apparatus to: assign a validation serial number to the reduced glyph font file; and verify validity of the request for the network document by: comparing the serial number included in the request for the network document to the validation serial number; and comparing the second set of glyphs included in the request for the network document to the specified set of glyphs included in the reduced glyph font file.
14. One or more non-transitory computer readable media storing computer readable instructions that, when executed, cause an apparatus to: receive, from a first client device, a request for a font; determine whether the request for the font specifies a set of glyphs that includes less than all glyphs defined for the font; in response to determining that the specified set of glyphs includes less than all of the glyphs defined for the font, generate a reduced glyph font file that includes only the specified set of glyphs; cache, at a font server different from the first client device, the reduced glyph font file in association with an identifier of a network document corresponding to the request for the font; receive, from a second client device, a request for the network document, wherein the request for the network document includes the identifier of the network document; and in response to receiving the request for the network document and based on the identifier of the network document, provide the cached reduced glyph font file to the second client device.