Some knowledge about text grid

I just checked the Office OpenXML file format and try to find the difference between the two types of text grid.

• linesAndChars (Line and Character Grid): Specifies that the parent section shall have both the additional line pitch and character pitch added to each line and character within it (as specified on the docGrid element (§2.6.5)) in order to maintain a specific number of lines per page and characters per line. When this value is set, the input specified via the user interface may be allowed in exact number of line/character pitch units.
• snapToChars (Character Grid Only) : Specifies that the parent section shall have both the additional line pitch and character pitch added to each line and character within it (as specified on the docGrid element (§2.6.5)) in order to maintain a specific number of lines per page and characters per line.When this value is set, the input specified via the user interface may be restricted to the number of lines per page and characters per line, with the consumer or producer translating this information based on the current font data to get the resulting line and character pitch values

OpenXML file format just specifies the difference of the user interface between these two types of text grid, while it doesn't piont out the difference of the layout behavior, especially for the layout behavior of Asian text and Webtern Text.

It seems that the author of the specification doen't know the essential difference between these two types of text grid. :-)
Currently, I am investigating the Document Grid specified in CSS3 mensioned by Florian.
http://www.w3.org/TR/2003/CR-css3-text-20030514/#document-grid