Senator Dianne Feinstein, the 90-year-old lawmaker from California, has given power of attorney to her daughter, according to a document posted by Insider — a step that is raising questions from some corners. 

Providing power of attorney to another person, typically a trusted family member or associate, isn't uncommon, and is often used as a way to accomplish certain legal or financial transactions, according to legal experts. 

But the report of Feinstein's daughter, Katherine Feinstein, 66, being given power of attorney for her mother comes after a moment of confusion for the democratic senator last month, when she began launching into remarks during a vote on an $823 billion military budget. Colleagues prompted her multiple times to simply vote "aye." 

Among the legal issues now being handled by the senator's only child is a family dispute over the senator's beach house near San Francisco, according to the New York Times. Feinstein wants to sell the home, a step opposed by the children of her late husband Richard C. Blum, the Times reported.

A spokesman for Feinstein declined to comment. "The senate office doesn't feel it's appropriate to comment on a private legal matter," he noted.

Here's what to know about the legal document.

What is a power of attorney? 

Power of attorney is a legal document "where one person gives another person the authority to act on their behalf just as as though they were in their shoes," noted Ashwani Prabhakar, a trusts and estates attorney at Davidoff Hutcher & Citron. 

Someone who has power of attorney doesn't need to be an actual attorney, he noted. Instead, the document makes another person the agent who can act on behalf of the "principal."

In Feinstein's case, the senator is considered the principal, and her daughter is her agent, Prabhakar noted.

What is a power of attorney used for?

The legal document can be used in a number of ways, ranging from single legal or financial transactions, such as a real estate closing, to providing people with more long-standing control over another person's affairs.

"Say I'm buying a house in another state, but I can't make it to the closing, so I might give power of attorney to my significant other to act on my behalf and sign the documents for me," Prabhakar noted. "And in that case, the power of attorney would actually spell that out."

But the document can also be used in case of situations where a person becomes incapacitated, he added. 

"It's what's called a springing power of attorney," he said. "It's a power of attorney that doesn't take any effect until something happens, and usually what that something is is two independent physicians declaring you incompetent, for example."

That can allow family members to get access to someone's bank accounts and pay their mortgage and other bills in case they are no longer able to do so themselves. 

Is it a commonly used document?

Absolutely, especially with people who are extremely wealthy or busy, Prabhakar noted. Feinstein is worth more than $95 million, according to Insider.

"A power of attorney alone is not an unusual thing," he noted. 

And executing a power of attorney can only occur when the principal is mentally competent, he added. "If you're mentally incapacitated, then you can't execute a power of attorney — it's too late," Prabhakar said.

He added, "Often how I see powers of attorneys used is by wealthy clients. They have so many finances and so many balls in the air that they sometimes give these limited powers of attorney to various people to handle things for them so that they can fly around the world and enjoy themselves."

What does the power of attorney mean for Feinstein?

In and of itself, not much, Prabhakar said. 

But, he added, "When you take that together with everything else that's going on and seen by the public, I can see why people are worried."

Still, the power of attorney would provide her daughter with the authority to act on her behalf, at least in some legal issues. 

"We know at least it gives her daughter the authority to be in the senator's shoes, in courtrooms, and to retain lawyers and tell them what to do and to pay them," he noted. "Other senators sitting with her probably have powers of attorneys that they've executed as well."

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• Dianne Feinstein