Word supports a Compatibility Mode in which it disables functionality not compatible with earlier versions of Word. Versions of Word prior to Word 2007 do not have native support for displaying Office Open XML Math. Instances of Office Open XML Math in Word documents are converted to pictures to preserve their visual fidelity when opened in versions of Word earlier than Word 2007. To do this, Word adds additional information to those pictures, using the equationxml attribute present on the shape element ("[ISO/IEC-29500-4] §188.8.131.52; shape (Shape Definition)"), to store the Office Open XML Math which represents the original equation/expression. If the document is removed from Compatibility Mode, the contents of this attribute are then used to replace the image with the specified equation/expression.
This document describes the format in which Word 2007, Word 2010, or earlier versions of Word with the Compatibility Pack, store Office Open XML Math content inside the equationxml attribute.