FORM tag specifies a fill-out form within an HTML
document.  More than one fill-out form can be in a single document,
but forms cannot be nested. 
<FORM ACTION="url"> ... </FORM> 
The attributes are as follows:
ACTION is the URL of the query server to which the
     form contents will be submitted; if this attribute is absent,
     then the current document URL will be used.
METHOD is the HTTP/1.0 method used to submit the
     fill-out form to a query server.  Which method you use depends on
     how your particular server works; we strongly recommend use of
     (or near-term migration to) POST.  The valid choices
     are:
GET -- this is the default method and causes the
     fill-out form contents to be appended to the URL as if they were
     a normal query.
POST -- this method causes the fill-out form
     contents to be sent to the server in a data body rather than as
     part of the URL.
ENCTYPE specifies the encoding for the fill-out form
     contents.  This attribute only applies if METHOD is
     set to POST -- and even then, there is only one
     possible value (the default,
     application/x-www-form-urlencoded) so far.
FORM you can have anything except another
FORM.  Specifically, INPUT,
SELECT, and TEXTAREA tags are used to
specify interface elements within the form. 
Forms are not automatically visually differentiated from the rest of a
document.  We recommend using the HR (horizontal rule)
tag before and after a form to cleanly differentiate it from
surrounding text and/or other forms. 
INPUT tag is used to specify a simple input element
inside a FORM.  It is a standalone tag; it does not
surround anything and there is no terminating tag -- i.e., it is used
in much the same way as IMG. 
In Mosaic for X, various types of INPUT tags are
instantiated as Motif widgets (text entry fields, toggle buttons,
pushbuttons, etc.). 
The attributes to INPUT are as follows: 
TYPE must be one of: 
NAME are grouped into
     "one of many" behavior)
NAME is the symbolic name (not a displayed name --
  normal HTML within the form is used for that) for this input field.
  This must be present for all types but "submit" and
  "reset", as it is used when putting together the query string
  that gets sent to the remote server when the filled-out form is
  submitted.
VALUE, for a text or password entry field, can be
     used to specify the default contents of the field.  For a
     checkbox or a radio button, VALUE specifies the
     value of the button when it is checked (unchecked
     checkboxes are disregarded when submitting queries); the default
     value for a checkbox or radio button is "on".  
     For types "submit" and "reset", VALUE can be used to
     specify the label for the pushbutton.
CHECKED (no value needed) specifies that this
     checkbox or radio button is checked by default; this is only
     appropriate for checkboxes and radio buttons.
SIZE is the physical size of the input field in
  characters; this is only appropriate for text entry fields and
  password entry fields.  If this is not present, the default is
  20.  Multiline text entry fields can be specified as
  SIZE=width,height; e.g. SIZE=60,12.
MAXLENGTH is the maximum number of characters that
  are accepted as input; this is only appropriate for text entry
  fields and password entry fields (and only for single-line text
  entry fields at that).  If this is not present, the default will be
  unlimited.  The text entry field is assumed to scroll appropriately
  if MAXLENGTH is greater than SIZE.
<FORM> ... </FORM>, any number of
SELECT tags are allowed, freely intermixed with other
HTML elements (including INPUT and TEXTAREA
elements) and text (but not additional forms).  In Mosaic for
X, SELECT tags are instantiated as Motif option menus and
scrolled lists. 
Unlike INPUT, SELECT has both opening
and closing tags.  Inside SELECT, only a sequence of
OPTION tags -- each followed by an arbitrary amount of
plain text (no HTML markup) -- is allowed; for example: 
        <SELECT NAME="a-menu">
        <OPTION> First option.
        <OPTION> Second option.
        </SELECT>
The attributes to SELECT are as follows: 
NAME is the symbolic name for this
     SELECT element.
  This must be present, as it is used when putting together the
  query string for the submitted form.
SIZE: if SIZE is
     1 or if the SIZE attribute is missing, by default
     the SELECT will be represented as a Motif option
     menu.  If SIZE is 2 or more, the SELECT
     will be represented as a Motif scrolled list; the value of
     SIZE then determines how many items will be visible.
MULTIPLE, if present (no value), specifies that the
     SELECT should allow multiple selections (n of
     many behavior).  The presence of MULTIPLE forces the
     SELECT to be represented as a Motif scrolled list,
     regardless of the value of SIZE.
OPTION are as follows: 
SELECTED specifies that this option is selected by
     default.  If the SELECT allows multiple selections
     (via the MULTIPLE attribute), multiple options can
     be specified as SELECTED.
TEXTAREA tag can be used to place a multiline text
entry field with optional default contents in a fill-out form.  The
attributes to TEXTAREA are as follows: 
NAME is the symbolic name of the text entry field.
ROWS is the number of rows (vertical height in
     characters) of the text entry field.
COLS is the number of columns (horizontal width in
     characters) of the text entry field.
TEXTAREA fields automatically have scrollbars; any amount
of text can be entered in them. 
The TEXTAREA element requires both an opening and
a closing tag.  A TEXTAREA with no default contents looks
like this: 
        <TEXTAREA NAME="foo" ROWS=4 COLS=40></TEXTAREA>
A TEXTAREA with default contents looks like this: 
        <TEXTAREA NAME="foo" ROWS=4 COLS=40>
        Default contents go here.
        </TEXTAREA>
The default contents must be straight ASCII text.  Newlines are
respected (so in the above example there will be a newline both
before and after "Default contents go here."). 
    action?name=value&name=value&name=value
("action" here is the URL specified by the
ACTION attribute to the FORM tag, or the
current document URL if no ACTION attribute was
specified.) Strange characters in any of the "name" or "value" instances will be escaped as usual; this includes "=" and "&". Note: This means that instances of "=" that separate names and values, and instances of "&" that separate name/value pairs, are not escaped.
For text and password entry fields, whatever the user typed in will be the value; if the user didn't type anything, the value will be empty but the "name=" part of the query string will still be present.
For checkboxes and radio buttons, the VALUE attribute
specifies the value of a checkbox or radio button when it is checked.
An unchecked checkbox is disregarded completely when assembling the
query string.  Multiple checkboxes can have the same NAME
(and different VALUEs), if desired.  Multiple radio
buttons intended to have "one of many" behavior should have the same
NAME and different VALUEs. 
GET method (above), but rather than appending them to the
URL specified by the form's ACTION attribute as a query,
the contents are sent in a data block as part of the POST
operation.  The ACTION attribute (if any) is the URL
to which the data block is POSTed. 
METHOD="POST", use 
     ACTION="http://hoohoo.ncsa.uiuc.edu/htbin-post/post-query"
METHOD="GET", use 
     ACTION="http://hoohoo.ncsa.uiuc.edu/htbin/query"
Important note: If you use the GET method in your
form, you will notice that the example GET server will
choke if too much data (more than a couple hundred bytes) is submitted
at a time -- the server is passing the data to the form-processing
module via a shell command line, and the maximum shell command line
length is being exceeded.  This problem does not exist with the
POST method and server. 
mailto URLs aren't supported as actions
  yet, and also the Mosaic 2.0 support only includes a subset of the
  allowable types of input fields (obviously "text" can also serve as
  "url", "int", "float", and "date" but without intrinsic range/error
  checking).
INPUT element of type
     TEXT (in which case Return in the text entry
     area submits the form) or at least one INPUT element
     of type IMAGE (in which case a click in the image
     submits the form).
NAME of the text field is "isindex", then
     the submitted query will be just like you are used to getting
     with ISINDEX -- "url?querystring" (i.e., not
     "url?isindex=querystring").  This allows you to use simple
     fill-out forms in your documents to point to existing query
     servers (including Gopher and WAIS servers!).  This of
     course assumes that the POST method is not specified
     for such forms.
ISINDEX tag differently.  Instead of having a
browser-interface method (dialog box or text field) for entering a
query, an instance of ISINDEX is instantiated as a
preloaded fill-out form suitable for entering a query; the form is
inlined at the location of the ISINDEX tag itself in
the document. Justifications for change:
ISINDEX document; this provides that
     very cleanly.
We strongly, strongly recommend use of the
POST method with fill-out forms.  One reason: with the
GET method, given the way many servers (e.g. NCSA httpd)
pass query strings from URLs to query server scripts, you run an
excellent chance of having the forms contents truncated by hardcoded
shell command argument lengths.  With POST (again, e.g.,
with NCSA httpd) you should be able to do a total end run around such
problems. 
NCSA httpd 1.0 (the official release) should be out shortly and will
contain an example POST fill-out form server.