EXPR: 
  EXPR + EXPR
  EXPR - EXPR
  EXPR * EXPR
  EXPR / EXPR
  EXPR && EXPR
  EXPR || EXPR
  - EXPR
  + EXPR
  ! EXPR
  ( EXPR )
  EXPR == EXPR
  EXPR != EXPR
  EXPR <= EXPR
  EXPR >= EXPR
  EXPR < EXPR
  EXPR > EXPR
  NUMBER
  RVAR

NUMBER:
  unsigned integer number

RVAR (Readable Variables):	
  images (integer)                  Total number of images being exported
  image_idx (integer)               Index of current image
  pages (integer)                   Total number of index pages being generated
  page_idx (integer)                Index number of current index page
  display_file_name_thumbnail
  display_file_name_image
  image_width
  image_height
  preview_width
  preview_height
  thumb_width
  thumb_height
  copy_originals (boolean)          Original images are being copied to the web 
                                    album output directory
  comment_visibility_image (bool)   Show comments on preview pages
  comment_visibility_index (bool)   Show comments on index pages
  place_visibility_image (bool)     Show place on preview pages
  place_visibility_index (bool)     Show place on index pages
  date_time_visibility_image (bool) Show date and time on preview pages
  date_time_visibility_index (bool) Show date and time on index pages
  file_name_visibility_image (bool) Show file name on image pages
  file_name_visibility_index (bool) Show file name on index pages
  image_dim_visibility_image (bool) Show image dimensions on image pages
  image_dim_visibility_index (bool) Show image dimensions on index pages
  file_size_visibility_image (bool) Show file size on image pages
  file_size_visibility_index (bool) Show file size on index pages
  exif_date_time_visibility_image (bool)      Show date and time (from exif 
                                              data) on image pages
  exif_date_time_visibility_index (bool)      Show date and time (from exif 
                                              data) on index pages
  exif_exposure_time_visibility_image (bool)  Show exposure time on image pages
  exif_exposure_time_visibility_index (bool)  Show exposure time on index pages
  exif_exposure_mode_visibility_image (bool)  Show exposure mode on image pages
  exif_exposure_mode_visibility_index (bool)  Show exposure mode on index pages
  exif_flash_visibility_image (bool)          Show flash mode on image pages
  exif_flash_visibility_index (bool)          Show flash mode on index pages
  exif_shutter_speed_visibility_image (bool)  Show shutter speed on image pages
  exif_shutter_speed_visibility_index (bool)  Show shutter speed on index pages
  exif_aperture_value_visibility_image (bool) Show aperture value on image pages
  exif_aperture_value_visibility_index (bool) Show aperture value on index pages
  exif_focal_length_visibility_image (bool)   Show focal length on image pages
  exif_focal_length_visibility_index (bool)   Show focal length on index pages
  exif_camera_model_visibility_image (bool)   Show camera model on image pages
  exif_camera_model_visibility_index (bool)   Show camera model on index pages

WVAR (Writable Variables):
  thumbnail_width (integer)         Output thumbnails of this width
  thumbnail_height (integer)        Output thumbnails of this height
  preview_width (integer)           Output preview images of this width
  preview_height (integer)          Output preview images of this height

---

<gthumb:title/>                     Display the album title.

<gthumb:image/>                     Display the image.
  idx="EXPR"
  idx_relative="EXPR"
  thumbnail="0/1"                   Display the image thumbnail (the
                                    image used in the index.html file).
  preview="0/1"                     Display the image preview (the
                                    image in the image.html file).
  max_size="EXPR"
  class="NAME"                      Assign CSS class NAME to image element
  id="NAME"                         Assign CSS id NAME to image element
  alt="TEXT"                        Assign alt text TEXT to image element

<gthumb:image_link/>                Display the image link
  idx="EXPR"
  idx_relative="EXPR"
  thumbnail="0/1"                   Display the image thumbnail link
  preview="0/1"                     Display the image preview link

<gthumb:image_idx/>
  idx_relative="EXPR"

<gthumb:image_dim/>
  idx="EXPR"
  idx_relative="EXPR"

<gthumb:images/>                    This tag gets substituted by the total
				    number of images.

<gthumb:file_name/>
  idx="EXPR"                        Display the filename of the image with 
				    index 'idx'.

  idx_relative="EXPR"               Display the filename of the image with 
				    index 'current_index + idx_relative'.
				    For example if idx_relative is -1 the 
				    filename of the previous image will be 
				    displayed.

  with_path="0/1"                   Display the full image path instead of the 
				    filename only.
				    For example '/home/joe/images/foo.jpg'
				    instead of 'foo.jpg'

  with_relative_path="0/1"          If with_path == 0 display the path relative
				    to the destination path.  
				    For example if the image path is
				    '/home/joe/images/foo.jpg' and the index is
				    saved as '/home/joe/public_html/index.html'
				    then this tag will be substituted by
				    '../images/foo.jpg'
                                    
  visibility="index/image/always"   Choose when to display this information:
                                    index:  Display this tag if the user 
				            chosen to display the filename 
				            in the index caption.
				    image:  Display this tag if the user
				            chosen to display the filename
					    in the image caption.
				    always: Always display this tag 
				            regardless of what the user 
					    chosen to display.

  utf8="0/1"                        Write in utf-8 format

<gthumb:file_path/>
  idx="EXPR"
  idx_relative="EXPR"
  relative_path="0/1"
  visibility="index/image/always"
  utf8="0/1"

<gthumb:file_size/>
  idx="EXPR"
  idx_relative="EXPR"
  visibility="index/image/always"

<gthumb:comment/>                   Display the comment for an image
  idx="EXPR"
  idx_relative="EXPR"
  max_size="EXPR"
  visibility="index/image/always"

<gthumb:place/>                     Display the place where an image was taken
  idx="EXPR"
  idx_relative="EXPR"
  max_size="EXPR"
  visibility="index/image/always"

<gthumb:date_time/>                 Display the time when an image was taken
  idx="EXPR"
  idx_relative="EXPR"
  max_size="EXPR"
  visibility="index/image/always"

<gthumb:exif:exposure_time/>
  idx="EXPR"
  idx_relative="EXPR"
  visibility="index/image/always"

<gthumb:exif:exposure_mode/>
  idx="EXPR"
  idx_relative="EXPR"
  visibility="index/image/always"

<gthumb:exif:flash/>
  idx="EXPR"
  idx_relative="EXPR"
  visibility="index/image/always"

<gthumb:exif:shutter_speed/>
  idx="EXPR"
  idx_relative="EXPR"
  visibility="index/image/always"

<gthumb:exif:aperture_value/>
  idx="EXPR"
  idx_relative="EXPR"
  visibility="index/image/always"

<gthumb:exif:focal_length/>
  idx="EXPR"
  idx_relative="EXPR"
  visibility="index/image/always"

<gthumb:exif:date_time/>
  idx="EXPR"
  idx_relative="EXPR"
  visibility="index/image/always"

<gthumb:exif:camera_model/>
  idx="EXPR"
  idx_relative="EXPR"
  visibility="index/image/always"

<gthumb:page_link/>
  idx="EXPR"
  idx_relative="EXPR"
  image_idx="0/1"

<gthumb:page_idx/>
  idx_relative="EXPR"

<gthumb:pages/>

<gthumb:table/>                     Output thumbnail blocks (thumbnail.gthtml) 
                                    inside an HTML table

<gthumb:thumbs/>                    Output thumbnail blocks (thumbnail.gthtml)
                                    without a surrounding table structure

<gthumb:date/>

<gthumb:set_var WVAR="EXPR" WVAR="EXPR" [..] />


---

<gthumb:text>                       Localized text.  You need to add the same
 [TEXT]                             text in the data/albumthemes/text.h file.
</gthumb:text>

---

<gthumb:if EXPR/> 
 [HTML]
<gthumb:else_if EXPR/> 
 [HTML]
<gthumb:else_if EXPR/> 
 [HTML]
.
.
.
<gthumb:else_if EXPR/> 
 [HTML]
<gthumb:else/> 
 [HTML]
<gthumb:end/>

---

<gthumb:eval/>
  idx=EXPR
  idx_relative=EXPR
  expr=EXPR                         Insert result of expression, maybe applied
                                    against given image info