> The packages constituting the diplomatic bag must bear visible external marks of their character and may contain only diplomatic documents or articles intended for official use.

But also part of Article 27

> The diplomatic bag shall not be opened or detained.

So you are stuck in a Catch 22. You suspect the bag doesn’t contain official documents or articles but without searching it you can not be sure.

If you believe the leaked documents they actually planned to smuggle Assange out using this method. https://www.wired.com/2015/09/ecuador-considered-smuggling-j...

How it’s usually handled is diplomatically. It’s reported to the higher ups, who will search the bag themselves but they can always refuse.

There are cases where a host country has opened diplomatic bags but they usually come with diplomatic protests.

There has been attempts to make Assange a diplomat of a country or two in an attempt to allow home to leave the embassy and leave the UK but the host country has to accept the status of a diplomat (usually done before they enter the country) and the UK government refused to recognise Assange's status still leaving him stuck.