diff --git a/README.md b/README.md
index 552c12e..13580d6 100644
--- a/README.md
+++ b/README.md
@@ -162,8 +162,9 @@ You can use autoload functions to define your own commands.
 command! -bang -nargs=* GGrep
   \ call fzf#vim#grep('git grep --line-number '.shellescape(<q-args>), 0, <bang>0)
 
-" We use VimEnter event so that the code is run after fzf.vim is loaded
-autocmd VimEnter * command! -bang Colors
+" Override Colors command. You can safely do this in your .vimrc as fzf.vim
+" will not override existing commands.
+command! -bang Colors
   \ call fzf#vim#colors({'left': '15%', 'options': '--reverse --margin 30%,0'}, <bang>0)
 
 " Augmenting Ag command using fzf#vim#with_preview function
@@ -173,7 +174,7 @@ autocmd VimEnter * command! -bang Colors
 "
 "   :Ag  - Start fzf with hidden preview window that can be enabled with "?" key
 "   :Ag! - Start fzf in fullscreen and display the preview window above
-autocmd VimEnter * command! -bang -nargs=* Ag
+command! -bang -nargs=* Ag
   \ call fzf#vim#ag(<q-args>,
   \                 <bang>0 ? fzf#vim#with_preview('up:60%')
   \                         : fzf#vim#with_preview('right:50%:hidden', '?'),
diff --git a/doc/fzf-vim.txt b/doc/fzf-vim.txt
index 6ba2478..e325553 100644
--- a/doc/fzf-vim.txt
+++ b/doc/fzf-vim.txt
@@ -187,9 +187,31 @@ You can use autoload functions to define your own commands.
     command! -bang -nargs=* GGrep
       \ call fzf#vim#grep('git grep --line-number '.shellescape(<q-args>), 0, <bang>0)
 
-    " We use VimEnter event so that the code is run after fzf.vim is loaded
-    autocmd VimEnter * command! Colors
+    " Override Colors command. You can safely do this in your .vimrc as fzf.vim
+    " will not override existing commands.
+    command! Colors
       \ call fzf#vim#colors({'left': '15%', 'options': '--reverse --margin 30%,0'})
+
+    " Augmenting Ag command using fzf#vim#with_preview function
+    "   * fzf#vim#with_preview([[options], preview window, [toggle keys...]])
+    "   * Preview script requires Ruby
+    "   * Install Highlight or CodeRay to enable syntax highlighting
+    "
+    "   :Ag  - Start fzf with hidden preview window that can be enabled with "?" key
+    "   :Ag! - Start fzf in fullscreen and display the preview window above
+    command! -bang -nargs=* Ag
+      \ call fzf#vim#ag(<q-args>,
+      \                 <bang>0 ? fzf#vim#with_preview('up:60%')
+      \                         : fzf#vim#with_preview('right:50%:hidden', '?'),
+      \                 <bang>0)
+
+    " Similarly, we can apply it to fzf#vim#grep. To use ripgrep instead of ag:
+    command! -bang -nargs=* Rg
+      \ call fzf#vim#grep(
+      \   'rg --column --line-number --no-heading --color=always '.shellescape(<q-args>), 1,
+      \   <bang>0 ? fzf#vim#with_preview('up:60%')
+      \           : fzf#vim#with_preview('right:50%:hidden', '?'),
+      \   <bang>0)
 <
 
 
diff --git a/plugin/fzf.vim b/plugin/fzf.vim
index 112cf62..b7955a7 100644
--- a/plugin/fzf.vim
+++ b/plugin/fzf.vim
@@ -33,7 +33,10 @@ function! s:defs(commands)
     return
   endif
   for command in a:commands
-    execute substitute(command, '\ze\C[A-Z]', prefix, '')
+    let name = ':'.prefix.matchstr(command, '\C[A-Z]\S\+')
+    if !exists(name)
+      execute substitute(command, '\ze\C[A-Z]', prefix, '')
+    endif
   endfor
 endfunction