add notational conventions for intervals

spec.html

@@ -1024,6 +1024,7 @@ <h1>Mathematical Operations</h1>
       <emu-note>
         <p><emu-eqn>floor(_x_) = _x_ - (_x_ modulo 1)</emu-eqn>.</p>
       </emu-note>
+      <p>An <dfn>interval</dfn> from lower bound _a_ to upper bound _b_ is a possibly-infinite, possibly-empty set of numeric values of the same numeric type. A numeric value _x_ is included in the interval if it satisfies the criteria _a_ &lt; _x_ and _x_ &lt; _b_. If the lower bound is described as inclusive, _a_ &lte; _x_ is used instead of _a_ &lt; _x_. If the upper bound is described as inclusive, _x_ &lte; _b_ is used instead of _x_ &lt; _b_. An <dfn>inclusive interval</dfn> is an interval where both bounds are inclusive. *NaN* is never included in an interval. An interval with an exclusive bound of *+0*<sub>𝔽</sub> or *-0*<sub>𝔽</sub> includes neither *+0*<sub>𝔽</sub> nor *-0*<sub>𝔽</sub>. An interval with an inclusive bound of *+0*<sub>𝔽</sub> or *-0*<sub>𝔽</sub> includes both *+0*<sub>𝔽</sub> and *-0*<sub>𝔽</sub>.</p>
     </emu-clause>
 
     <emu-clause id="sec-value-notation">