<subsetOfRealsInput>

<subsetOfRealsInput> is a block-level interactive widget that renders a number line on which the learner builds a subset of the real numbers. The learner can click to add or remove points, drag to extend intervals, and toggle endpoints between open and closed.

The value of the widget is a <subsetOfReals> — so it compares equal to another subset when the two represent the same set, and can be plugged into a <when> condition for answer validation.

A few caveats unusual among Doenet’s input-shaped components:

• Despite its name, <subsetOfRealsInput> does not inherit from the Input base class. As a result it cannot be placed inside an <answer>; for answer validation, name it, leave it outside the <answer>, and reference it from an <award> via referencesAreResponses plus a <when> check.
• It is block-level, so it cannot sit inside a <p>.
• It currently accepts no children — including no <label> or <shortDescription>. Place any prompt text in a sibling <p> above the widget. See Doenet/DoenetML#1167 for the accessibility follow-up.

Attributes and Properties

Examples

Example: A simple subset input

<p>Build a subset of the real line:</p>
 
<subsetOfRealsInput name="S" />
 
<p>You selected <m>S = $S</m>.</p>

The default <subsetOfRealsInput> shows a number line from $-10$ to $10$ on which the learner can build a subset. The current value is referenced with $S, returning a <subsetOfReals>.

Example: Use in answer validation

<p>Shade the set of <m>x</m> for which <m>x^2 \leq 4</m>.</p>
 
<subsetOfRealsInput name="userSet" />
 
<answer name="ans">
  <award referencesAreResponses="$userSet">
    <when>
      $userSet = <subsetOfReals>[-2, 2]</subsetOfReals>
    </when>
  </award>
</answer>

The widget itself sits outside the <answer> (placing it inside would render nothing — see the caveat above). The <award> names $userSet as a response via referencesAreResponses, then a <when> child compares the referenced subset against the expected [-2, 2]. Any equivalent representation of $[-2, 2]$ is accepted because = on subsets compares the sets, not their syntactic form.

Attribute Examples

Attribute Example: prefill

<p>Edit the prefilled subset:</p>
 
<subsetOfRealsInput name="S" prefill="(-1, 3]" />
 
<p><m>S = $S</m></p>

prefill provides an initial subset (in the input’s format). The learner sees the prefilled subset and can edit it from there.

Attribute Example: variable

<p>Choose a set of times <m>t</m>:</p>
 
<subsetOfRealsInput name="S" variable="t" prefill="t > 0" />
 
<p>As an interval: <m>S = $S</m></p>
<p>As inequalities:
  <m><subsetOfReals extend="$S" displayMode="inequalities"/></m>
</p>

variable does two things. It names the symbol the input expects when parsing a prefill string — with variable="t" set, prefill="t > 0" parses to the set $\\{t : t > 0\\} = (0, \infty)$; with the default x it would fail because t would be an unknown symbol. And it propagates through extend to a <subsetOfReals>, so rendering the same subset with displayMode="inequalities" uses t for the variable in the inequality.