descriptive chemical formula (property)

{
    "$id": "https://schemas.optimade.org/defs/v1.2/properties/optimade/structures/chemical_formula_descriptive",
    "$schema": "https://schemas.optimade.org/meta/v1.2/optimade/property_definition.json",
    "title": "descriptive chemical formula",
    "x-optimade-type": "string",
    "x-optimade-definition": {
        "label": "chemical_formula_descriptive_optimade_structures",
        "kind": "property",
        "version": "1.2.0",
        "format": "1.2",
        "name": "chemical_formula_descriptive"
    },
    "type": [
        "string",
        "null"
    ],
    "description": "The chemical formula for a structure as a string in a form chosen by the API implementation.\n\n**Requirements/Conventions**:\n\n- The chemical formula is given as a string consisting of properly capitalized element symbols followed by integers or decimal numbers, balanced parentheses, square, and curly brackets `(`,\\ `)`, `[`,\\ `]`, `{`, `}`, commas, the `+`, `-`, `:` and `=` symbols.\n  The parentheses are allowed to be followed by a number.\n  Spaces are allowed anywhere except within chemical symbols.\n  The order of elements and any groupings indicated by parentheses or brackets are chosen freely by the API implementation.\n- The string SHOULD be arithmetically consistent with the element ratios in the `chemical_formula_reduced` property.\n- It is RECOMMENDED, but not mandatory, that symbols, parentheses and brackets, if used, are used with the meanings prescribed by [IUPAC's Nomenclature of Organic Chemistry](https://www.qmul.ac.uk/sbcs/iupac/bibliog/blue.html).\n\n**Query examples**:\n\n- Note: the free-form nature of this property is likely to make queries on it across different databases inconsistent.\n- A filter that matches an exactly given formula: `chemical_formula_descriptive=\"(H2O)2 Na\"`.\n- A filter that does a partial match: `chemical_formula_descriptive CONTAINS \"H2O\"`.",
    "examples": [
        "(H2O)2 Na",
        "NaCl",
        "CaCO3",
        "CCaO3",
        "(CH3)3N+ - [CH2]2-OH = Me3N+ - CH2 - CH2OH"
    ],
    "x-optimade-unit": "inapplicable"
}