56. A computer readable medium encoded with a computer program for constructing a text document, the computer program comprising instructions that when executed by a programmable processor of a computer cause the programmable processor to perform operations comprising: receiving user input at the computer selecting a character for insertion into a text document; identifying in a memory of the computer a glyphlet representing the selected character, the glyphlet being a data structure including both a set of one or more character attributes defining semantic information of the selected character and a set of one or more glyph attributes defining appearance information for a glyph representative of the selected character, the glyph attributes including all the information necessary to render a glyph image of the glyph; inserting the character into the text document by inserting a reference to the identified glyphlet into a text document, where the reference can be used to access the sets of character and glyph attributes from the glyphlet for the character selected by the user input; and displaying the character in the text document, the displayed character being rendered from the glyph attributes.
56. A computer readable medium encoded with a computer program for constructing a text document, the computer program comprising instructions that when executed by a programmable processor of a computer cause the programmable processor to perform operations comprising: receiving user input at the computer selecting a character for insertion into a text document; identifying in a memory of the computer a glyphlet representing the selected character, the glyphlet being a data structure including both a set of one or more character attributes defining semantic information of the selected character and a set of one or more glyph attributes defining appearance information for a glyph representative of the selected character, the glyph attributes including all the information necessary to render a glyph image of the glyph; inserting the character into the text document by inserting a reference to the identified glyphlet into a text document, where the reference can be used to access the sets of character and glyph attributes from the glyphlet for the character selected by the user input; and displaying the character in the text document, the displayed character being rendered from the glyph attributes. 57. The computer readable medium encoded with the computer program of claim 56 , wherein: user input selecting a character includes user input selecting a glyph shape representing the character.