html_scheme
-----------
Qt QWebEngineUrlScheme https://doc.qt.io/qt-5/qwebengineurlscheme.html
Alternative web page schemes can be registered using the manager/provider
mechanishm in bundle_info.xml.
To register a URL scheme, add a provider in a bundle's bundle_info.xml:
::
The required parts are the *name* of scheme and the *manager* **url_schemes**.
There are optional keyword arguments to the provider that give access to
all of the customization options of the QWebEngineUrlScheme class (see its
documentation for details).
defaultPort: int
Set default port.
path: str
One of **Path**, **Host**, **HostAndPort**, or **HostPortAndUserInformation**.
flag: boolean
The flag can be one of **SecureScheme**, **LocalScheme**, **LocalAccessAllowed**,
**NoAccessAllowed**, **ServiceWorkersAllowed**, **ViewSourceAllowed**,
or **ContentSecurityPolicyIgnored**.
The boolean should be **true**, **1**, or **on**.