I am refering to the book - Mechanics of Materials by Beer, Johnston and DeWolf (McGraw-Hill) topic 8.2.

When we design a wide-flange beam, we must consider two conditions. First, the shear stress at the maximum shear section must not exceed the allowable shear stress. Second, the principal stress at the junction of the web and the flange at the section of the maximum moment must also be compared to the allowable normal stress. This is straightforward and clear to me.