1 ==========================
2 HTML Templating Mechanisms
3 ==========================
5 :Version: $Revision: 1.5 $
7 Current Situation and Issues
8 ============================
10 Syntax
11 ------
13 Roundup currently uses an element-based HTML-tag-alike templating syntax::
15 <display call="checklist('status')">
17 The templates were initially parsed using recursive regular expression
18 parsing, and since no template tag could be encapsulate itself, the parser
19 worked just fine. Then we got the ``<require>`` tag, which could have other
20 ``<require>`` tags inside. This forced us to move towards a more complete
21 parser, using the standard python sgmllib/htmllib parser. The downside of this
22 switch is that constructs of the form::
24 <tr class="row-<display call="plain('status')">">
26 don't parse as we'd hope. It would be almost impossible to modify the sgmllib
27 parser to parse the above "correctly", so a wholly new parser would be
28 required. That is a large undertaking, and doesn't address another couple of
29 issues that have arisen:
31 1. the template syntax is not well-formed, and therefore is a pain to parse
32 and doesn't play well with other tools, and
33 2. user requirements generally have to be anticipated and accounted for in
34 templating functions (like ``plain()`` and ``checklist()`` above), and
35 we are therefore artificially restrictive.
37 Arguments for switching templating systems:
39 *Pros*
41 - more flexibility in templating control and content
42 - we can be well-formed
44 *Cons*
46 - installed user base (though they'd have to edit their templates with the
47 next release anyway)
48 - current templating system is pretty trivial, and a more flexible system
49 is likely to be more complex
52 Templates
53 ---------
55 We should also take this opportunity to open up the flexibility of the
56 templates through:
58 1. allowing the instance to define a "page" template, which holds the overall
59 page structure, including header and footer
63 Possible approaches
64 ===================
66 Zope's PageTemplates
67 --------------------
69 Using Zope's PageTemplates seems to be the best approach of the lot.
70 In my opinion, it's the peak of HTML templating technology at present. With
71 appropriate infrastructure, the above two examples would read:
73 <span tal:replace="item/status/checklist">status checklist</span>
75 <tr tal:attributes="class string:row-${item/status/name}">
77 ... which doesn't look that much more complicated... honest...
79 Other fun can be had when you start playing with stuff like:
81 <table>
82 <tr tal:repeat="message item/msg/list">
83 <td tal:define="from message/from">
84 <a href="" tal:attributes="href string:mailto:${from/address}"
85 tal:content="from/name">mailto link</a>
86 </td>
87 <td tal:content="message/title">subject</td>
88 <td tal:content="message/created">received date</td>
89 </tr>
90 </table>
93 Implementation
94 ~~~~~~~~~~~~~~
96 I'm envisaging an infrastructure layer where each template has the following
97 variables defined:
99 *class*
100 the current class of node being displayed
101 *item*
102 the current node from the database, if we're viewing a specific node
103 (*classname*)
104 the current node is also available under its classname, so a *user* node
105 would also be available under the name *user*.
106 *form*
107 the current CGI form information
108 *instance*
109 the current instance
110 *db*
111 the current open database
112 *config*
113 the current instance config
114 *util*
115 utility methods
117 Accesses through a class (either through *class* or *db.<classname>*):
119 class HTMLItem:
120 def __getattr__(self, attr):
121 ''' return an HTMLItem instance '''
122 def classhelp(self, ...)
123 def list(self, ...)
125 Accesses through an *item*::
127 class HTMLItem:
128 def __getattr__(self, attr):
129 ''' return an HTMLItem instance '''
130 def history(self, ...)
131 def classhelp(self, ...)
132 def remove(self, ...)
134 String, Number, Date, Interval HTMLProperty
135 a wrapper object which may be stringified for the current plain() behaviour
136 and has methods emulating all the current display functions, so
137 ``item/name/plain`` would emulate the current ``call="plain()``". Also,
138 ``python:item.name.plain(name=value)`` would work just fine::
140 class HTMLProperty:
141 def __init__(self, instance, db, ...)
142 def __str__(self):
143 return self.plain()
145 class StringHTMLProperty(HTLProperty):
146 def plain(self, ...)
147 def field(self, ...)
148 def stext(self, ...)
149 def multiline(self, ...)
150 def email(self, ...)
152 class NumberHTMLProperty(HTMLProperty):
153 def plain(self, ...)
154 def field(self, ...)
156 class BooleanHTMLProperty(HTMLProperty):
157 def plain(self, ...)
158 def field(self, ...)
160 class DateHTMLProperty(HTMLProperty):
161 def plain(self, ...)
162 def field(self, ...)
163 def reldate(self, ...)
165 class IntervalHTMLProperty(HTMLProperty):
166 def plain(self, ...)
167 def field(self, ...)
169 Link HTMLProperty
170 the wrapper object would include the above as well as being able to access
171 the class information. Stringifying the object itself would result in the
172 value from the item being displayed. Accessing attributes of this object
173 would result in the appropriate entry from the class being queried for the
174 property accessed (so item/assignedto/name would look up the user entry
175 identified by the assignedto property on item, and then the name property of
176 that user)::
178 class LinkHTMLProperty(HTMLProperty):
179 ''' Be a HTMLItem too '''
180 def __getattr__(self, attr):
181 ''' return a new HTMLProperty '''
182 def download(self, ...)
183 def checklist(self, ...)
185 Multilink HTMLProperty
186 the wrapper would also be iterable, returning a wrapper object like the Link
187 case for each entry in the multilink::
189 class MultilinkHTMLProperty(HTMLProperty):
190 def __len__(self):
191 ''' length of the multilink '''
192 def __getitem(self, num):
193 ''' return a new HTMLItem '''
194 def checklist(self, ...)
195 def list(self, ...)
197 *util*
198 the util object will handle::
200 class Util:
201 def __init__(self, ...)
202 def filterspec(self, ...)
203 def note(self, ...)
204 def submit(self, ...)
206 Action
207 ======
209 1. Investigate how PageTemplates would be integrated into Roundup:
211 - we could go for a fully-divorced-from-Zope approach, which would involve
212 bundling PageTemplates/TAL/ZTUtils in with Roundup, with all the
213 Zope-specific bits removed.
214 - we could try to coexist with a Zope installation, but there the problem
215 would be that Zope includes its own copy of PageTemplates/TAL/ZTUtils and
216 we'd be installing a version in site-packages, which would be bad.
218 The latter may allow nicer integration with Zope itself, giving Zope
219 Roundup users access to acquired information in their templates. We could
220 get around that by modifying the ZRoundup interface to use the "real Zope"
221 ZPT. Maybe.
223 2. Implement the Roundup infrastructure described in the `implementation`_
224 above.