+Let us add keywords as a searchable field.
+#+BEGIN_SRC emacs-lisp :tangle org-ref.el
+(setq helm-bibtex-additional-search-fields '(keywords))
+#+END_SRC
+
+Next, we are going to add keywords to the helm interface. This modifies the helm-bibtex function to add our keywords.
+#+BEGIN_SRC emacs-lisp :tangle org-ref.el
+(defun helm-bibtex-candidates-formatter (candidates source)
+ "Formats BibTeX entries for display in results list."
+ (cl-loop
+ with width = (with-helm-window (window-width))
+ for entry in candidates
+ for entry = (cdr entry)
+ for entry-key = (helm-bibtex-get-value entry 'entry-key)
+ for fields = (--map (helm-bibtex-clean-string
+ (helm-bibtex-get-value entry it " "))
+ '(author title year has-pdf has-note entry-type))
+ for fields = (-update-at 0 'helm-bibtex-shorten-authors fields)
+ for fields = (append fields
+ (list (or (helm-bibtex-get-value entry 'keywords)
+ "" )))
+ collect
+ (cons (s-format "$0 $1 $2 $3 $4$5 $6" 'elt
+ (-zip-with (lambda (f w) (truncate-string-to-width f w 0 ?\s))
+ fields (list 36 (- width 85) 4 1 1 7 7)))
+ entry-key)))
+#+END_SRC
+
+Next, we add some functions to add keywords to a bibtex entry using a helm interface, and a new action to add keywords to entries from helm-bibtex.
+#+BEGIN_SRC emacs-lisp :tangle org-ref.el
+;; adapted from bibtex-utils.el
+;; these are candidates for selecting keywords/tags
+(defun org-ref-bibtex-keywords ()
+ "Get keywords defined in current bibtex file.
+These are in the keywords field, and are comma or semicolon separated."
+ (save-excursion
+ (goto-char (point-min))
+ (let (keywords kstring)
+ (while (re-search-forward "^\\s-*keywords.*{\\([^}]+\\)}" nil t)
+ ;; TWS - remove newlines/multiple spaces:
+ (setq kstring (replace-regexp-in-string "[ \t\n]+" " " (match-string 1)))
+ (mapc
+ (lambda (v)
+ (add-to-list 'keywords v t))
+ (split-string kstring "\\(,\\|;\\)[ \n]*\\|{\\|}" t)))
+ keywords)))
+
+
+(defun org-ref-set-bibtex-keywords (keywords &optional arg)
+ "Add KEYWORDS to a bibtex entry.
+If KEYWORDS is a list, it is converted to a comma-separated string. The KEYWORDS are added to the beginning of the field. Otherwise KEYWORDS should be a string of comma-separate keywords."
+ (interactive "sKeywords: \nP")
+ (bibtex-set-field
+ "keywords"
+ (if arg
+ ;; replace with arg
+ (if (listp keywords)
+ (mapconcat 'identity keywords ", ")
+ keywords)
+ ;; else concatentate
+ (concat
+ (if (listp keywords)
+ (mapconcat 'identity keywords ", ")
+ keywords)
+ (when (not (string= "" (bibtex-autokey-get-field "keywords")))
+ (concat ", " (bibtex-autokey-get-field "keywords"))))))
+ (save-buffer))
+
+
+(defun helm-tag-bibtex-entry ()
+ "Helm interface to add keywords to a bibtex entry.
+Run this with the point in a bibtex entry."
+ (interactive)
+ (let ((keyword-source `((name . "Existing keywords")
+ (candidates . ,(org-ref-bibtex-keywords))
+ (action . (lambda (candidate)
+ (org-ref-set-bibtex-keywords
+ (mapconcat
+ 'identity
+ (helm-marked-candidates)
+ ", "))))))
+ (fallback-source `((name . "Add new keywords")
+ (dummy)
+ (action . (lambda (candidate)
+ (org-ref-set-bibtex-keywords helm-pattern)
+ )))))
+ (helm :sources '(keyword-source fallback-source))))
+
+(defun helm-bibtex-show-entry (key)
+ "Show the entry in the BibTeX file.
+The original function in helm-bibtex has a bug where it finds the
+first key that partially matches. This version avoids that."
+ (catch 'break
+ (dolist (bibtex-file (if (listp helm-bibtex-bibliography)
+ helm-bibtex-bibliography
+ (list helm-bibtex-bibliography)))
+ (let ((buf (helm-bibtex-buffer-visiting bibtex-file))
+ (entries '()))
+ (find-file bibtex-file)
+ (bibtex-map-entries
+ (lambda (key start end)
+ (add-to-list 'entries (cons key start))))
+ (if (assoc key entries)
+ (progn
+ (goto-char (cdr (assoc key entries)))
+ (throw 'break t))
+ (unless buf
+ (kill-buffer)))))))
+
+(defun org-ref-helm-tag-entries (candidates)
+ "Set tags on selected bibtex entries from helm-bibtex.
+User is prompted for tags. This function is called from `helm-bibtex'."
+ (message "")
+ (let ((keywords (read-input "Keywords (comma separated): ")))
+ (loop for key in (helm-marked-candidates)
+ do
+ (save-window-excursion
+ (helm-bibtex-show-entry key)
+ (bibtex-set-field
+ "keywords"
+ (concat
+ keywords
+ ", " (bibtex-autokey-get-field "keywords")))
+ (save-buffer)))))
+#+END_SRC
+
+Next, adapt the helm-bibtex source with these features:
+