The value that author enter should saved but when I again revisit the textarea setting(cq:dialog) the value is not saved it is blank.
Please refer the below for cq dialog.xml:
<textarea
jcr:primaryType="nt:unstructured"
jcr:title="Text"
sling:resourceType="granite/ui/components/foundation/section"
class="cq-dialog-coe-toggle-tab_target textarea">
<layout
jcr:primaryType="nt:unstructured"
sling:resourceType="granite/ui/components/foundation/layouts/fixedcolumns"
margin="{Boolean}false"/>
<items jcr:primaryType="nt:unstructured">
<column
jcr:primaryType="nt:unstructured"
sling:resourceType="granite/ui/components/foundation/container">
<items jcr:primaryType="nt:unstructured">
<placeholder
jcr:primaryType="nt:unstructured"
sling:resourceType="granite/ui/components/foundation/form/textfield"
fieldLabel="Placeholder"
name="./placeholder"/>
<maxlength
jcr:primaryType="nt:unstructured"
sling:resourceType="granite/ui/components/foundation/form/textfield"
fieldLabel="Maxlength"
name="./maxlength"/>
</items>
</column>
</items>
</textarea>