social/base_search_mail_content/views/trgm_index_view.xml

<?xml version="1.0" encoding="utf-8"?>
<odoo>

    <record model="ir.ui.view" id="trgm_index_view_form">
        <field name="name">trgm.index.view.form</field>
        <field name="model">trgm.index</field>
        <field name="inherit_id" ref="base_search_fuzzy.trgm_index_view_form"/>
        <field name="arch" type="xml">
            <field name="field_id" position="attributes">
                <attribute name="domain">[('ttype', 'in', ['char', 'text', 'html'])]</attribute>
                <attribute name="help">"You can either select a field of type 'text', 'char' or 'html'."</attribute>
          </field>
      </field>
    </record>

    <record model="ir.ui.view" id="trgm_index_view_tree">
        <field name="name">trgm.index.view.tree</field>
        <field name="model">trgm.index</field>
        <field name="inherit_id" ref="base_search_fuzzy.trgm_index_view_tree"/>
        <field name="arch" type="xml">
            <field name="field_id" position="attributes">
                <attribute name="help">"You can either select a field of type 'text', 'char' or 'html'."</attribute>
          </field>
      </field>
    </record>

</odoo>