Correct the claim in the docs that if_(c)[p] has attribute type

optional<ATTR(p)>; it actually has attribute type ATTR(p).

Fixes #278.

Author: tzlaine

doc/rationale.qbk

@@ -261,9 +261,8 @@ Also, Spirit-style looseness is more complicated than `parser` above
 indicates.  Remember, `int_ | eps` and `-int_` are supposed to be semantically
 equivalent.  To do otherwise this would be a profound violation of the
 principle of least surprise.  So, if they're equivalent, we would need to
-apply the same rule to `int_ | eps`.  Also, we would probably need to apply it
-to `if_(cond)[int_]`, which is also a `std::optional<int>`.  This is a lot to
-remember, and this is complicated to implement and maintain.
+apply the same rule to `int_ | eps`.  This is a lot to remember, and this is
+complicated to implement and maintain.
 
 I've been using Spirit 1 and later Spirit 2 since they were released.  I did
 not know about the particular looseness discussed here; a user pointed it out

doc/tables.qbk

@@ -319,7 +319,7 @@ the input they match unless otherwise stated in the table below.]
 
     [[ `_if_np_(pred)[p]` ]
      [ Equivalent to `_e_(pred) >> p`. ]
-     [ `std::optional<_ATTR_np_(p)>` ]
+     [ `_ATTR_np_(p)` ]
      [ It is an error to write `_if_np_(pred)`.  That is, it is an error to omit the conditionally matched parser `p`. ]]
 
     [[ `_sw_np_(arg0)(arg1, p1)(arg2, p2) ...` ]
@@ -557,7 +557,7 @@ tables below:
 
     [[`_rpt_np_(arg0)[p]`]              [`std::string` if `_ATTR_np_(p)` is `char` or `char32_t`, otherwise `std::vector<_ATTR_np_(p)>`]]
     [[`_rpt_np_(arg0, arg1)[p]`]        [`std::string` if `_ATTR_np_(p)` is `char` or `char32_t`, otherwise `std::vector<_ATTR_np_(p)>`]]
-    [[`_if_np_(pred)[p]`]               [`std::optional<_ATTR_np_(p)>`]]
+    [[`_if_np_(pred)[p]`]               [`_ATTR_np_(p)`]]
     [[`_sw_np_(arg0)(arg1, p1)(arg2, p2)...`]
      [`std::variant<_ATTR_np_(p1), _ATTR_np_(p2), ...>`]]
 ]