[Evolution] Hard to translate string in Evolution

[ÐÐÐÐÑÐÐÐÑÑ ÐÐÐÐÐ <ash contact bg>]

There is a string in Evolution that I cannot understand and translate. I
also cannot comprehend the translator comment.

Can anyone give advice?

#. Translators: '=' and ';' should not be changed but ASCII
#: ../plugins/email-custom-header/apps_evolution_email_custom_header.schemas.in.h:4
msgid ""
"[Security=Personal;Unclassified;Protected;InConfidence;Secret;Topsecret]"

What does this mean and when is it used? It seems that it is in
schema-file and this complicates things further.

Kind regards:
al_shopov