Actual (live) results in your browser:

ab



Expected results (screenshot 450px wide):
An 'a' at the left side of a box and a 'b' at the right side

Nota bene: The "b" letter should be inside the dotted <p>, not below.

Markup code and CSS code are:
p {border: dotted 2px #FFE4E1;}
<P>a<SPAN style="float: right">b</SPAN></P>

This example directly comes from the latest CSS 2.1 specification, at section 9.5.1 on "Positioning the float: the 'float' property"