Explicit doi in a separate tag

[rodionstepanov]

Hi! Plugin is very nice but Crossref does not resolve DOI from resolved_reference unstructured citation.
Is it possible to get DOI in a separated tag? For example

<citation key="19158">
<doi> 10.2118/191177-MS</doi>
<unstructured_citation>Bao Y., He L., Lv X., Shen Y.., Liu Z., Yang Z. Proc. of the SPE Trinidad and Tobago section energy resources conference. Port of Spain, Trinidad and Tobago, June 25-26, 2018. SPE-191177-MS. https://doi.org/10.2118/191177-MS</unstructured_citation>
</citation>