nfse-nacional/nfse-php ? reverse-engineered prompt

Build me a PHP SDK for integrating with NFS e Nacional, using a certificate file and environment choice like homologation or production.

I want it to let me create a context once, then work with two main flows, one for companies that issue invoices and one for city halls or tax offices. For the company side, I need to send a DPS, issue an NFS e, check an invoice by access key, download documents, get the DANFSE PDF, register events like cancellation, and consult agreement parameters. For the municipality side, I need to download documents, look up a taxpayer, and consult parameters and tax rates.

Please make it handle the XML and data objects cleanly, and include a few working examples I can copy and run. If some endpoint details vary by city, make that easy to configure, and look up current docs online if you need to.