eg undefined types, functions, constants, members, variables.
Yes this would be ideal, if nothing else can be done, because for example anyone working in WordPress theme development and only have their theme folder as their project, _every single WP function_ shows up as undefined.
It is a bit unfortunate however to have to turn off checking for undefined symbols when really they aren't undefined technically. :)

@onetrev I'll ship some wp stubs in a future release #833
Is there a workaround for this currently? Just updated and realized this is an issue...
https://github.com/bmewburn/intelephense-docs/issues/2
This fixes most problems but doesn't seem to include core constants.
@wkoehn the wordpress stubs package author may accept a request for this or a PR.
@bmewburn Thanks, I'll look into it a bit deeper. For now, I just included WP core in my workspace folders and it has no problems parsing that. I'd prefer an updated stubs package of course but this gets me going for now. I love the extension and just purchased pro!
New settings added in 1.3.3:
intelephense.diagnostics.undefinedTypes
intelephense.diagnostics.undefinedFunctions
intelephense.diagnostics.undefinedConstants
intelephense.diagnostics.undefinedClassConstants
intelephense.diagnostics.undefinedMethods
intelephense.diagnostics.undefinedProperties
intelephense.diagnostics.undefinedVariables
1.2 only had undefined variable diagnostics. Disabled all the others will give 1.2 behaviour.
Most helpful comment
New settings added in 1.3.3:
intelephense.diagnostics.undefinedTypesintelephense.diagnostics.undefinedFunctionsintelephense.diagnostics.undefinedConstantsintelephense.diagnostics.undefinedClassConstantsintelephense.diagnostics.undefinedMethodsintelephense.diagnostics.undefinedPropertiesintelephense.diagnostics.undefinedVariables1.2 only had undefined variable diagnostics. Disabled all the others will give 1.2 behaviour.