diff --git a/README.org b/README.org
index 2d7f300..3ceaef3 100644
--- a/README.org
+++ b/README.org
@@ -75,6 +75,8 @@ Installing with [[https://framagit.org/steckerhalter/quelpa][Quelpa]] is easy:
 
 # These links work on GitHub's Org renderer but not in Org.
 
+If user search bare string, the predicate ~org-ql-plain-string-predicate~ will be used by default.
+
 Feedback on these APIs is welcome.  Eventually, after being tested and polished, they will be considered stable. 
 
 # TODO: Find a way to get these examples included in the info manual.
@@ -531,6 +533,8 @@ Simple links may also be written manually in either sexp or non-sexp form, like:
 /Note:/ The next release, 0.5, may include changes which will require minor updates to written queries (e.g. a few predicates may be renamed).  Users who wish to avoid those changes happening unexpectedly in their configs should avoid upgrading =org-ql= beyond 0.4 automatically, as they will be pushed to the =master= branch when ready.
 
 *Added*
++  *Variable*
+     -  ~org-ql-plain-string-predicate~, which will be used when user search bare string.
 +  *Commands*
      -  ~helm-org-ql-views~, which shows one of ~org-ql-views~ selected with Helm.
      -  ~org-ql-search~ can search files in ~org-directory~; customization options are available in the ~org-ql-search~ group.
diff --git a/org-ql.el b/org-ql.el
index 9dad848..c4068d1 100644
--- a/org-ql.el
+++ b/org-ql.el
@@ -129,6 +129,9 @@ the value returned by it at that node.")
     "Plist of predicates, their corresponding functions, and their docstrings.
 This list should not contain any duplicates."))
 
+(defvar org-ql-plain-string-predicate 'regexp
+  "Plain strings in queries are matched with this predicate.")
+
 ;;;; Customization
 
 (defgroup org-ql nil
@@ -588,8 +591,9 @@ Or, when possible, fix the problem."
 
 (defun org-ql--pre-process-query (query)
   "Return QUERY having been pre-processed.
-Replaces bare strings with (regexp) selectors, and appropriate
-`ts'-related selectors."
+Replaces bare strings with predicate set by
+`org-ql-plain-string-predicate' , and appropriate `ts'-related
+selectors."
   ;; This is unsophisticated, but it works.
   ;; TODO: Maybe query pre-processing should be done in one place,
   ;; rather than here and in --query-predicate.
@@ -605,7 +609,7 @@ Replaces bare strings with (regexp) selectors, and appropriate
                      (`(unless ,condition . ,clauses) `(unless ,(rec condition)
                                                          ,@(mapcar #'rec clauses)))
                      ;; TODO: Combine (regexp) when appropriate (i.e. inside an OR, not an AND).
-                     ((pred stringp) `(regexp ,element))
+                     ((pred stringp) `(,org-ql-plain-string-predicate ,element))
                      ;; Quote children queries so the user doesn't have to.
                      (`(children ,query) `(children ',query))
                      (`(children) '(children (lambda () t)))
@@ -1776,7 +1780,8 @@ Builds the PEG expression using predicates defined in
                             (-sort (-on #'> #'length)))))
       `(cl-defun org-ql--plain-query (input &optional (boolean 'and))
          "Return query parsed from plain query string INPUT.
-Multiple predicates are combined with BOOLEAN."
+Multiple predicates are combined with BOOLEAN.
+If no predicates are found, `org-ql-plain-string-predicate' will be used."
          (unless (s-blank-str? input)
            (let* ((query (org-ql--peg-parse-string
                           ((query (+ term
@@ -1787,7 +1792,7 @@ Multiple predicates are combined with BOOLEAN."
                                      positive-term))
                            (positive-term (or (and predicate-with-args `(pred args -- (cons (intern pred) args)))
                                               (and predicate-without-args `(pred -- (list (intern pred))))
-                                              (and plain-string `(s -- (list 'regexp s)))))
+                                              (and plain-string `(s -- (list org-ql-plain-string-predicate s)))))
                            (plain-string (or quoted-arg unquoted-arg))
                            (predicate-with-args (substring predicate) ":" args)
                            (predicate-without-args (substring predicate) ":")