Sim, sua interpretação está correta.

Para fins de explicação, usaremos Lua Argêntea:

The Wards of Silverymoon

The city of Silverymoon is protected by a powerful magical effect called a mythal. This potent form of elven high magic forbids the casting of several types of spells, causes other spells to be permanently in effect, and allows the denizens of Silverymoon to use still other spells with a word. The mythal’s effects cover the city itself, plus an area 1,000 yards beyond its limits in all directions (even up into the sky and down into the earth).

Spells with the death, evil, or teleportation descriptor, conjuration (summoning) spells, and evocation [fire] spells are all forbidden by the mythal of Silverymoon. Any attempt to cast such a spell fails automatically, though the spell slot is used up normally.

Existe uma classe de prestígio élfico que lida especificamente com esses mythals, chamada de Spellguard of New Silverymoon .

Fonte: Guia do Jogador para Faerun

Mito Drannor é / foi uma cidade élfica, que utilizou os mesmos tipos de mythals de segurança. Segundo a Wikipedia:

Myth Drannor, formerly known as Cormanthor the City of Song, was once considered to be the most beautiful and peaceful of any of the cities in Faerûn. At its peak, no city could compare to the glory of Myth Drannor. All races lived in complete harmony for the first time in memory, without fear or corruption. However, the city has been in ruins for many years. The city was once protected by a device called a mythal which is one of the greatest spells in perhaps all of the Realms. The mythal is a protective spell which shields Myth Drannor from outside forces and from general harm.