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Answer Manipulation

Five rule features that shape the answers themselves: what they default to, how options are presented, and which options remain visible to subsequent respondents.

FeatureAuthored onRuns
Pre-fill / defaultQuestion → Advanced tabClient (render time)
Pipe valueQuestion text fields (titles, descriptions, option labels)Client (render time)
Carry-forward optionsRule (carry_forward action)Client (render time)
Randomize / rotateQuestion → Advanced tabClient. Per-respondent, stable across reloads.
Quota / capRule (quota action)Client hide plus server enforce

Pre-fill / default value​

Seed a question's initial answer from one of three sources, evaluated in order. The first non-empty source wins. The respondent can always overwrite the pre-filled value; the chain only fires when no answer exists yet.

Authoring​

Question Inspector → Advanced tab → Pre-fill / default value section.

Click Add prefill source and pick one of:

KindReads fromExample
URL parameter?<name>=<value> on the survey page URL?utm_campaign=summer-2026 seeds campaign_id
Earlier answerThe respondent's answer to another question in this surveyQ1 "Your name" seeds Q12 "Confirm name"
Contact fieldThe signed-in Joomla user's profile: name, email, username, or idAuto-populate "Your email" for logged-in users

Source chain semantics​

You can stack multiple sources on one question. The engine tries each in order, and the first to return a non-empty value seeds the answer. If none resolve (anonymous visitor, missing URL param, the earlier answer is blank), the question stays empty for the respondent to fill in.

Example: fall back gracefully​

Question: "Your email"
Sources (in order):
  1. URL parameter: email
  2. Contact field: email

A visitor opening /survey?email=alice@example.com gets alice@example.com regardless of login state. A logged-in visitor without that URL parameter gets the email from their Joomla profile. An anonymous visitor with no parameter sees an empty field.

URL parameter security​

Parameter names are sanitised on save. Only [A-Za-z0-9_-] is allowed, with a 64-character cap. The raw URL value goes straight into the answer field, so the question's existing validation (regex, required, etc.) still applies. There is no "trust the URL because it came from the URL" loophole.

Pipe value​

Inject a respondent's answer into later question text. Use cases:

  • "Earlier you said you live in {{city}}. What's your zip code?"
  • "How would you rate the {{product_picked.label}} for value?"
  • "Tell us about your {{role}} experience."

Syntax​

PlaceholderResolves to
{{field_key}}The respondent's answer to that question: text value, picked option label, or empty string
{{field_key.label}}For choice questions, the picked option's human label
{{field_key.value}}For choice questions, the picked option's stable key (yes, red, option_2, etc.)
{{field_key|Fallback}}Use "Fallback" when the field is empty. Survives the case where the respondent hasn't answered yet.

Where you can pipe​

SurfaceSupported
Question title✅
Question description✅
Option labels✅
Validation error messages✅
Email templates (follow-up invitation, notify)✅

Example: dynamic option labels​

Q1: "Which products did you buy?"  (checkbox)
  □ Coffee maker
  □ Toaster
  □ Blender

Q2 (per product): "Rate the {{Q1.label}}"

Q2's title updates as the respondent fills in Q1. Choice-family answers pipe the picked option's label by default; use .value if you want the stable key.

Fallback gotcha​

If you reference a question that hasn't been answered yet, the placeholder evaluates to the fallback, or to an empty string if you didn't supply one. Always include a fallback for any pipe that could fire before its source is answered:

"Hi {{first_name|there}}, …"

This renders "Hi there," for visitors who haven't typed their name yet.

Carry-forward options​

Narrow a target question's options to those the respondent picked (or did not pick) in an earlier multi-pick question.

Authoring​

Add a rule on any question, set action to Carry-forward options. The popover asks for:

FieldDescription
From (source)A multi-pick question: checkbox, rank, or image_multi
Into (target)Any choice-family question: radio, checkbox, dropdown, image, etc.
ModeInclude selected (only show picked options) or Exclude selected (hide picked options)

Two patterns​

Include, "rate what you used":

Q4 "Which features do you use?" (checkbox)
  ☑ Search
  ☐ Calendar
  ☑ Messaging
  ☐ Profile

Q6 "Rate each feature you use" (matrix, rows = features)
  Carry-forward: Q4 → Q6 rows, mode: include

Q6 only shows rows for "Search" and "Messaging".

Exclude, "which one didn't you try":

Q4 "Which features did you try?" (checkbox)
  ☑ A
  ☑ B
  ☐ C

Q7 "Pick a feature you haven't tried" (radio)
  Carry-forward: Q4 → Q7, mode: exclude

Q7 only offers "C".

Composition with quotas​

Carry-forward and quota share the same option-filter pipeline at render time. A carry-forward rule narrows the list, then any quota rule removes options that have hit their cap. The respondent only ever sees options that pass both filters.

Randomize / rotate​

Shuffle a question's options per respondent. The shuffle is deterministic: the same respondent always sees the same order, so reloads and resume-from-email do not surprise them. Different respondents see different orders.

Authoring​

Question Inspector → Advanced tab → Randomization section.

ControlWhat it does
Shuffle options per respondent (checkbox)Turns randomization on
Always show last (option list)Pick options that should appear at the end regardless of shuffle

"Always last" pins​

For options like Other or Prefer not to say, you want them randomized out of the way of the real choices but still visible, ideally always at the bottom so respondents trained on form patterns find them.

Tick each option you want pinned; pinned options appear in the order you ticked them, after the shuffled remainder.

Pinning requires a saved option (so the stable option_key exists). Brand-new options get a "(save the question first to enable pinning)" hint until they round-trip through the server.

How the shuffle stays stable​

The engine seeds a per-respondent random by combining hashes of responseId and questionId (XOR'd, Wang-style mixer) and runs a Fisher-Yates shuffle. The same respondent submitting the same survey on a different day still gets the same order on each question.

Question type support​

Any question with an options array: radio, checkbox, dropdown, image, image_multi, rank. Matrix rows and cols are not yet shuffleable. The indices are part of the answer's serialised shape.

Quota / cap​

Once N respondents have picked an option, hide it for everyone else.

Authoring​

Add a rule on any question, set action to Quota / cap option. The popover asks for:

FieldDescription
Target questionThe choice-family question carrying the cap
OptionWhich option to cap (picker reads from the question's option list)
CapMaximum number of respondents who can pick this option. 0 means "always full", useful as a hard kill switch.

How it works​

  1. Render time (client): The SPA hits siteApi.quotaAvailability(surveyId) every 60 seconds and filters at-cap options out of the rendered choice list. Already-full options simply don't appear.
  2. Submit time (server): Even if a tampered client tries to submit a capped option, the server runs an atomic UPDATE … SET count = count + 1 WHERE count < cap. The rows-affected count tells the server whether the slot was claimed. Lost races return HTTP 409 with a quota_full payload identifying the option.

Example: workshop sign-ups​

Q "Pick a workshop time"  (radio)
  9 AM, 11 AM, 1 PM, 3 PM

Rules:
  When option = 9 AM, quota cap 20
  When option = 11 AM, quota cap 20
  When option = 1 PM, quota cap 20
  When option = 3 PM, quota cap 20

Once 20 people pick 9 AM, that radio button disappears for the 21st respondent. If two people submit simultaneously and only one slot remains, the server picks one winner and 409s the other with a banner suggesting another time.

Composition with carry-forward​

Carry-forward narrows options first; quota then removes at-cap options. Both filters compose in a single render-time pass, with no double scanning and no flicker.

Counter behaviour​

Counters live in #__survey_option_counters. Manual reset (e.g. "open a new batch of slots") is currently a SQL operation; an admin UI for it is on the roadmap.