While Musavi has long supported the manifesto, the signature of popular opposition leader and cleric Karubbi is a first for the document, which is being circulated by the main opposition Green Movement.
The charter is meant to explain the identity and goals of the Green Movement. It also calls for a representative government, limits executive powers, fully supports the demands and legitimacy of the women's movement, ensures protection for the country's numerous religious and ethnic minorities while also addressing the needs of workers, farmers, and servicemen.
Musavi adviser Ardeshir Amir Arjomand told RFE/RL's Radio Farda in an interview last week that this was "definitely not the final version" of the charter, which, he said, was "meant to evolve along with the opposition movement itself."
Still, Karrubi's signature gives the hotly debated charter additional credibility and further unites the opposition. The former presidential candidate is a towering figure among the opposition due to his leading role in mass protests that shook Iran following the disputed June 2009 reelection of Iranian President Mahmud Ahmadinejad.
Arjomand said the charter discussed "the implementation of the [existing] constitution as a whole" as a way to demand key political reforms.
"Without limiting the power of the government, the constitution doesn't work," he said. "This is what's been forgotten by all the current institutions and government organizations: the rights of the nation, the system of a republic on which this constitution is based."
But first, Iran needed "free and fair elections," he said. "Only then can the people choose their future; and if they decide to change the constitution, or modify and reform it, they have the right to do it and no one can oppose their will."
Arjomand said this is the reason for the Green Movement's opposition to approbative supervision, an interpretation of the constitution that allows institutions like the Guardians Council to veto laws that have popular support.
Return Of The Green Movement
In recent weeks, inspired by antigovernment protesters in Tunisia and Egypt, Musavi and Karrubi called for an opposition protest in defiance of a government ban. The February 14 demonstration was the largest seen in Iran since the government's brutal crackdown on unrest in the summer of last year.
The rally galvanized the opposition, which is now calling for weekly demonstrations set to begin in March
But the road ahead looks tough for Iran's opposition. The government is skilled at cracking down on protest activity, so when -- as now -- key opposition leaders are barred from direct communication, activists turn to old videos and recordings of past speeches.
The following short film, made last summer, is one example. It has seen a resurrection online recently in the wake of new protest activity, perhaps because it focuses on many of the same themes as the much-discussed Green Movement charter and features some of Musavi's early calls for political reform (for English subtitles, click "cc"):
-- Kristin Deasy and Hannah Kaviani