Sanders proposed changing the rules governing GRATs “and other types of trusts and valuation techniques,” citing reports that billionaires have used GRATs and similar techniques to save about $100 billion in taxes since 2000.

Life insurance agents and other financial professionals with few high-net-worth clients may have wondered what the reference to GRATs was all about, and whether that had anything to do with them.

Now that Sanders has included the idea of changing the GRAT rules in such a high-profile financing idea document, it might play a more prominent role in conversations about changing the tax code.

Here’s a look at answers to five basic GRAT questions financial professionals need to understand to talk about the topic.

1. So, what exactly is a GRAT?

A GRAT is a vehicle an individual, or grantor, can use to transfer property.

The grantor creates an irrevocable trust. The grantor then puts property into the trust, for a specified period of time, in exchange for getting fixed payments, every year or more often, from the trust. The value of the fixed payments is based on the fair market value of the property put in the trust.

If the trust period expires before the grantor dies, any value still in the trust goes to the trust beneficiary. The Internal Revenue Service treats the value that goes to the beneficiary as a gift.

In the trust period expires after the grantor dies, then the GRAT assets become part of the grantor’s estate.

A grantor who uses a GRAT may be able to avoid having to pay estate taxes or gift taxes on the appreciated value of the property transferred into the GRAT.

The value of the tax break a GRAT can provide depends on the level of the official interest rate used to value the grantor’s retained interest. The lower the official rate used in the valuations, the more successful the GRAT will be.

(Related: The Clock Is Ticking on GRATs)

A shorter trust term also helps increase the odds that the GRAT will succeed in lowering overall taxes.

2. How does anyone know what’s in the GRATs?

GRATs have been getting attention partly because some high-profile executives at high-profile publicly traded companies have put their companies’ securities GRATs, and filed routine reports on those transactions with the U.S. Securities and Exchange Commission.

The Washington Post, for example, published a 2013 article with the headline “GRAT shelters: An accidental tax break for America’s wealthiest,” and used SEC filings to show that GRAT users include people like Mark Zuckerberg, the chief executive officer of Facebook, and LLoyd Blankfein, the chief executive officer of Goldman Sachs.

3. What have the Democrats said and done about GRATs in the past?

Former President Barack Obama has been proposing tightening the GRAT rules in annual budget proposals for years. Many of the proposals have involved lengthening the amount of time that the trust used in the GRAT must stay in effect, rather than eliminating the GRAT strategy altogether.

In 2015, Sanders included a GRAT provision proposing to make the minimum term of a GRAT longer in his Responsible Estate Tax Act bill.

In August, the IRS proposed a package of Estate, Gift and Generation-Skipping Transfer Taxes regulations. The regulations did not directly refer to GRATs, but a coalition of groups that included the AFL-CIO and Americans for Democratic Action argued in a comment on that draft that the IRS should proceed to “close loopholes like the Grantor Retained Annuity Trust.”

4. What has President Donald Trump’s administration had to say about GRATs?

The Trump administration and Treasury Secretary Steven Mnuchin have not expressed any specific hostility aimed at GRATs, but they are trying to develop and pass a sweeping tax code simplification package that could have effects on GRATs that are difficult to predict.

5. Why does a doomed proposal floated by Bernie Sanders matter?

One reason to keep track of this issue is proposals can kick around Washington for many years before becoming law. Advocates of health savings accounts, for example, spent years on unfruitful efforts to get an HSA law, and eventually, got Congress to approve the birth of HSAs.

Another reason is that, even if GRAT proposals circulate for years, without getting anywhere, talk about the topic could put financial services groups on the defensive.

Financial services groups and financial services professionals could have to spend time lobbying against GRAT tightening proposals when they would prefer to be talking about new tax incentives for retirement savers, for the purchase of private long-term care insurance, or for other cherished goals.