'''[http://www.openmath.org/%|%OpenMath]''' is a standard for exchange of mathematical objects, currently (2014) at version 2.

In the future, OpenMath3 is expected to be equivalent to strict Content-[MathML]3; both of these standards are under construction. It is mostly MathML that has been changed to match OpenMath.

Basic OpenMath tags (node types):
   '''OMI''':   Integer
   '''OMF''':   Floating-point number (64-bit IEEE, i.e., a [double])
   '''OMV''':   Variable
   '''OMS''':   Symbol defined in some external ''Content Dictionary'' (CD).
   '''OMA''':   Application (like function application)

Composite OpenMath expressions are usually constructed as an OMA whose first child is the symbol denoting the operation or function, e.g.

======none
<OMA>
    <OMS cd="arith1" name="plus"/>
    <OMI> 2 </OMI>
    <OMF dec="3.4e5"/>
    <OMV name="y"/>
</OMA>
======

which is analogous to `[expr] {2+3.4e5+$y}`. If parsed by [a little XML parser] (or [tdom]), this (modulo whitespace) comes out as

======
OMA {} {{OMS {cd arith1 name plus} {}} {OMI {} {{#text 2}}} {OMF {dec 3.4e5} {}} {OMV {name y} {}}}
======

which is not too onerous to process in Tcl.

There are also some more advanced tags:

   '''OMSTR''', '''OMB''':   Strings and bytearrays
   '''OMBIND''', '''OMBVAR''':   Used when binding variables (like ''x'' is bound by the integral in ∫₁³ ''x''² d''x'').
   '''OMATTR''', '''OMATP''':   Used for putting attributions on subexpressions.
   '''OME''':   Errors
   '''OMFOREIGN''':   Foreign format data
   '''OMR''':   References (for sharing subexpressions, much like [Tcl_Obj]s can be shared)


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