With $25 billion in total assets, the Vanguard High Dividend Yield ETF (NYSEMKT:VYM) is one of the most popular exchange-traded funds among investors who want exposure to the stock market as well as a steady stream of income. Whether you currently invest in the fund or not, here are seven things you may be surprised to learn.

1. It's 92% cheaper than the average fund

The Vanguard High Dividend Yield ETF has a low 0.08% expense ratio, which is 92% lower than the average fund with similar holdings, according to data from Morningstar.

That means that for every $10,000 you have invested, you're paying only $8 annually in investment fees, a remarkably low amount. In fact, this low fee structure is the primary reason Warren Buffett refers to index funds as the best investment most Americans can make.

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2. You might be able to invest commission-free

If you invest in the Vanguard High Dividend Yield ETF through a Vanguard brokerage account, you won't pay a penny in trading commissions when you invest in the fund. The same goes for any other Vanguard ETF. This can save you hundreds of dollars or more over the long run.

Even if you don't have a Vanguard brokerage account, many online brokers have started offering a selection of commission-free ETFs, and the Vanguard High Dividend Yield ETF may be on the list. To name one example, I use TD Ameritrade to invest, and a quick check shows that I can invest in the ETF commission-free through my TD Ameritrade IRA.

3. It's also available as a mutual fund

You may also be interested to know that the Vanguard High Dividend Yield ETF is also available in mutual fund form, the Vanguard High Dividend Yield Index Fund Investor Shares (NASDAQMUTFUND: VHDYX).

The mutual fund version has a $3,000 minimum initial investment, and a slightly higher 0.15% expense ratio. It's offered by many retirement and education savings plans and may be of interest to individual investors as well, especially if the ETF isn't available commission-free through your broker.

4. The ETF is 5-Star rated by Morningstar

Under the Morningstar fund rating system, which uses a scale of one to five stars, only the top 10% of funds in a given category are given the top five-star rating.

In the Large Value category, the Vanguard High Dividend Yield ETF has a five-star rating over three-year and 10-year time periods, as well as a four-star rating over the past five years, all of which combine to give the fund an overall five-star rating.

5. The ETF has a weighted portfolio

Although the Vanguard High Dividend Yield ETF has 428 stocks in its portfolio as of May 31, 2017, it's important to note that the index the fund tracks is weighted. In other words, larger companies make up a larger portion of the index, and therefore of the fund's portfolio.

In fact, the fund's 10 largest holdings, which includes such companies as Microsoft, Johnson & Johnson, and ExxonMobil, make up more than 30% of the fund's net assets.

6. The fund excludes one of the highest-paying sectors

The Vanguard High Dividend Yield ETF tracks an index that invests in stocks with above-average dividend yields, the FTSE High Dividend Yield Index.

Real estate investment trusts, or REITs, are some of the highest-paying dividend stocks in the market, so you might expect them to be included in a "high yield" ETF. However, REITs are notably absent from the Vanguard High Dividend Yield ETF and the index it tracks.

In fact, the benchmark specifically excludes REITs, mainly due to their tax structure. Specifically, REIT dividends generally don't qualify for the favorable tax rates applied to qualified dividends. So, if you want to invest in REITs, you'll need to look elsewhere.

7. High-dividend stocks can beat the market during crashes

Stocks that pay dividends tend to outperform their non-dividend counterparts during stock market corrections and crashes. There are a few possible reasons. For one thing, dividend stocks tend to be more established and mature businesses, that tend to have steadier revenue streams. So, during tough times, they tend not to take as much of a profitability hit as high-growth non-dividend stocks.

Furthermore, steady, reliable dividends tend to help support a stock's price during crashes. As a simplified example, let's say that a stock trades for $50 and yields 5%. If the stock's price were to fall to $25, the dividend would now translate to a 10% yield, and income-seeking investors would come pouring in, creating upward pressure on the stock's price.

To illustrate this point, consider that the S&P 500 generated a total negative return of 36.1% during 2008. Meanwhile, the Vanguard ETF lost value but outperformed the index, with a negative total return of 32.4%.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.