Require a space after colon instead of tab for fixed width area.

src/parser/util.rs

@@ -1,4 +1,5 @@
 use nom::branch::alt;
+use nom::bytes::complete::is_a;
 use nom::character::complete::anychar;
 use nom::character::complete::line_ending;
 use nom::character::complete::none_of;
@@ -228,9 +229,16 @@ where
     }
 }
 
+/// Match at least one space character.
+///
+/// This is similar to nom's space1 parser except space1 matches both spaces and tabs whereas this only matches spaces.
+pub(crate) fn only_space1<'s>(input: OrgSource<'s>) -> Res<OrgSource<'s>, OrgSource<'s>> {
+    is_a(" ")(input)
+}
+
 /// Match single space or tab.
 ///
-/// In org-mode syntax, spaces and tabs are interchangeable.
+/// In org-mode syntax, spaces and tabs are often (but not always!) interchangeable.
 pub(crate) fn org_space<'s>(input: OrgSource<'s>) -> Res<OrgSource<'s>, char> {
     one_of(" \t")(input)
 }