src/Bootstrap/Elements/InputGroup.php
public function prefix($prefix, $isPlainText = true)
    {
        if ($prefix === null)
        {
            return $this;
        }

        $element = clone $this;
        $element->prefixes[] = [
            'content'   => $prefix,
            'plaintext' => $isPlainText,
        ];

        return $element;
    }
public function prefix($prefix, $isPlainText = true)
    {
        if ($prefix === null)
        {
            return $this;
        }

        $element = clone $this;
        $element->prefixes[] = [
            'content'   => $prefix,
            'plaintext' => $isPlainText,
        ];

        return $element;
    }
Add an addon before the field

@param string|\Spatie\Html\BaseElement $prefix      One or more prefixes to append before the field
@param bool                            $isPlainText Is the prefix to be handled like a button, dropdown, etc.

@return static