Equation Editor is a legacy formula editor developed by Design Science that allows users to construct math and science equations in a WYSIWYG environment. It is included in most word processors (e.g. Microsoft Word), presentation programs (e.g. Microsoft PowerPoint), and many other products. Equation Editor is a simplified version of Design Science MathType. There are an estimated 4 million Equation Editor users world wide.

Equation Editor did not significantly change from 1991 to 2007. For Microsoft Office 2007, the old Equation Editor is included as is, however Office 2007 applications include a reengineered equation editor with support for a TeX-like linear input/edit language called "Office Math Markup Language" (Office MathML or OMML) in addition to its WYSIWYG interface. The revised equation editor is built into the document-editing part of the interface instead of being operated through a separate dialog and being treated as an OLE object in the document. Unicode Plain Text Encoding of Mathematics is also supported. Office Math Markup Language (OMML) is a mathematical markup language embedded in WordProcessingML, with intrinsic support for including word processing markup like revision markings, footnotes, comments, images and elaborate formatting and styles.

Format compatibility

The OMML format is different from the World Wide Web Consortium (W3C) MathML recommendation. Academic publishers have noted that the rendering of equations as graphics in .DOCX files impairs its usability for scholarly publishing as the conversion to and from MathML to OMML while converting between DOC and DOCX is not seamless and automatic. Especially, when saving DOC files using Word 2007, equations are rendered as graphics as the older DOC format as well as older versions of Office do not support OMML, which prevents editing and flexibly printing the equations. OMML is partially compatible with MathML through comparatively simple XSL Transformations. Word 2007 has support for converting equations to/from MathML via the clipboard. Copied equations are in (Presentation) MathML format, so they can be pasted into other programs that understand this XML markup, such as Mathematica. Conversely, MathML can also be pasted into a Word document and it will be recognized as an equation and displayed properly (as long as it does not contain MathML symbolic character entities such as &PlusMInus; - use numeric entities instead). The transformations that allow copying/pasting equations via MathML are driven by two XSL stylesheets (omml2mml.xsl and mml2omml.xsl). These scripts can be used outside of Word by reading or manipulating DOCX XML files directly. Equation number management is also possible using macros.