fix godoc

Author: PeterIvanov

error_113.go

@@ -6,7 +6,7 @@ import "errors"
 
 // IsOfType is a type check for errors.
 // Returns true either if both are of exactly the same type, or if the same is true for one of current type's ancestors.
-// For an error that does not have an errorx type, returns false.
+// For an error that does not have an errorx type, returns false unless it wraps another error of errorx type.
 func IsOfType(err error, t *Type) bool {
 	e := burrowForTyped(err)
 	return e != nil && e.IsOfType(t)
@@ -16,6 +16,7 @@ func IsOfType(err error, t *Type) bool {
 // IsOfType is a proper type check for an errorx-based errors.
 // It takes the transparency and error types hierarchy into account,
 // so that type check against any supertype of the original cause passes.
+// It also tolerates non-errorx errors in chain if those errors support go 1.13 errors unwrap.
 func (e *Error) IsOfType(t *Type) bool {
 	cause := e
 	for cause != nil {