Explanation

Code 18 is used to indicate that ChemML markup has been provided for chemical formulas and equations.

No reading systems provide support for rendering ChemML, however, and EPUB does not support the format without fallbacks, so this code is more of a placeholder for possible future use.

Examples

Example 1 — ChemML markup provided 
<ProductFormFeature>
   <ProductFormFeatureType>09</ProductFormFeatureType>
   <ProductFormFeatureValue>18</ProductFormFeatureValue>
</ProductFormFeature>

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