in csp/utils.py [0:0]
def _async_attr_mapper(attr_name: str, val: str | bool) -> str:
"""The `async` attribute works slightly different than the other bool
attributes. It can be set explicitly to `false` with no surrounding quotes
according to the spec."""
if val in [False, "False"]:
return f" {attr_name}=false"
elif val:
return f" {attr_name}"
else:
return ""