[css2] changed "reference box" to containing block

added example of how to use 'position: fixed' to do frames-like layout

commented out a paragraph of dubious value

some clarifications added

description of 'display' property upgraded

no change to syntax or anything

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extra : convert_revision : svn%3A73dc7c4b-06e6-40f3-b4f7-9ed1dbc14bfc/trunk%40545

Author: howcom