Explicit may only be specified along with a dstring formal parameter. The modifier makes the compiler check that an actual parameter is a non-indexed BDL string variable. Any other string notations are not allowed.
dll "some.dll"
"DoExplicit"
function DoExplicit(sVar : in dstring explicit);
dcltrans
transaction TMain
var
s1 : string;
hMem : number;
begin
DoExplicit(s1); // ok
DoExplicit(s1[2]); // compiler error
DoExplicit(in hMem); // compiler error
DoExplicit("hello"); // compiler error
DoExplicit("\h110022"); // compiler error
end TMain;