update docstrings

Author: lucaferranti

src/intervals/intervals.jl

@@ -95,7 +95,7 @@ end
 """
     interval(a, b)
 
-`interval(a, b)` checks whether [a, b] is a valid `Interval`, which is the case if `-∞ <= a <= b <= ∞`, using the (non-exported) `is_valid_interval` function. If so, then an `Interval(a, b)` object is returned; if not, then an error is thrown.
+`interval(a, b)` checks whether [a, b] is a valid `Interval`, using the (non-exported) `is_valid_interval` function. If so, then an `Interval(a, b)` object is returned; if not, a warning is printed and the empty interval is returned.
 """
 function interval(a::T, b::S) where {T<:Real, S<:Real}
     if !is_valid_interval(a, b)

src/intervals/macros.jl

@@ -1,20 +1,21 @@
 # This file is part of the IntervalArithmetic.jl package; MIT licensed
 
-"""The `@interval` macro is the main method to create an interval.
-It converts each expression into a narrow interval that is guaranteed to contain the true value passed by the user in the one or two expressions passed to it.
+"""The `@interval` macro converts an expression into a narrow interval that is guaranteed to contain the true value of the expression.
 When passed two expressions, it takes the hull of the resulting intervals
 to give a guaranteed containing interval.
 
 Examples:
 ```
-    @interval(0.1)
-
-    @interval(0.1, 0.2)
-
-    @interval(1/3, 1/6)
+    @interval sin(0.1) + cos(0.2)
+```
 
-    @interval(1/3^2)
+is equivalent to
 ```
+    sin(0.1..0.1) + cos(0.2..0.2)
+```
+
+NOTE! `@interval` should be used only to create intervals from an expression, as in the example
+before. To construct an interval from single numbers, the `..` is preferred, e.g. `0.1..0.2`
 """
 macro interval(expr1)
     make_interval(:(parameters.precision_type), expr1, ())