How to add multiple font files for the same font?

I'm looking at the MDC page for the @font-face CSS rule, but I don't get one thing. I have separate files for bold, italic and bold + italic. How can I embed all three files in one @font-face rule? For example, if I have:

@font-face {
    font-family: "DejaVu Sans";
    src: url("./fonts/DejaVuSans.ttf") format("ttf");
}
strong {
    font-family: "DejaVu Sans";
    font-weight: bold;
}

The browser will not know which font to be used for bold (because that file is DejaVuSansBold.ttf), so it will default to something I probably don't want. How can I tell the browser all the different variants I have for a certain font?

The solution seems to be to add multiple @font-face rules, for example:

@font-face {
    font-family: "DejaVu Sans";
    src: url("fonts/DejaVuSans.ttf");
}
@font-face {
    font-family: "DejaVu Sans";
    src: url("fonts/DejaVuSans-Bold.ttf");
    font-weight: bold;
}
@font-face {
    font-family: "DejaVu Sans";
    src: url("fonts/DejaVuSans-Oblique.ttf");
    font-style: italic, oblique;
}
@font-face {
    font-family: "DejaVu Sans";
    src: url("fonts/DejaVuSans-BoldOblique.ttf");
    font-weight: bold;
    font-style: italic, oblique;
}

By the way, it would seem Google Chrome doesn't know about the format("ttf") argument, so you might want to skip that.

(This answer was correct for the CSS 2 specification. CSS3 only allows for one font-style rather than a comma-separated list.)

As of CSS3, the spec has changed, allowing for only a single font-style. A comma-separated list (per CSS2) will be treated as if it were normal and override any earlier (default) entry. This will make fonts defined in this way appear italic permanently.

@font-face {
    font-family: "DejaVu Sans";
    src: url("fonts/DejaVuSans.ttf");
}
@font-face {
    font-family: "DejaVu Sans";
    src: url("fonts/DejaVuSans-Bold.ttf");
    font-weight: bold;
}
@font-face {
    font-family: "DejaVu Sans";
    src: url("fonts/DejaVuSans-Oblique.ttf");
    font-style: italic;
}
@font-face {
    font-family: "DejaVu Sans";
    src: url("fonts/DejaVuSans-BoldOblique.ttf");
    font-weight: bold;
    font-style: italic;
}
@font-face {
    font-family: "DejaVu Sans";
    src: url("fonts/DejaVuSans-Oblique.ttf");
    font-style: oblique;
}
@font-face {
    font-family: "DejaVu Sans";
    src: url("fonts/DejaVuSans-BoldOblique.ttf");
    font-weight: bold;
    font-style: oblique;
}

In most cases, italic will probably be sufficient and oblique rules won't be necessary if you take care to define whichever you will use and stick to it.

To have font variation working correctly, I had to reverse the order of @font-face in CSS.

@font-face {
    font-family: "DejaVuMono";
    src: url("styles/DejaVuSansMono-BoldOblique.ttf");
    font-weight: bold;
    font-style: italic, oblique;
}   
@font-face {
    font-family: "DejaVuMono";
    src: url("styles/DejaVuSansMono-Oblique.ttf");
    font-style: italic, oblique;
}
@font-face {
    font-family: "DejaVuMono";
    src: url("styles/DejaVuSansMono-Bold.ttf");
    font-weight: bold;
}
 @font-face {
    font-family: "DejaVuMono";
    src: url("styles/DejaVuSansMono.ttf");
}