> ## Documentation Index
> Fetch the complete documentation index at: https://doc.lucidworks.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Fallback Parser Stage

export const schema = {
  "type": "object",
  "title": "Fallback",
  "description": "If no previous parser stage was able to handle the stream, the fallback parser will copy the data into the _raw_content_ field for later parsing and analysis.",
  "required": ["type"],
  "properties": {
    "id": {
      "type": "string",
      "title": "Parser ID",
      "default": "eea53b52-1374-4ee1-97df-e900d6f2879b"
    },
    "label": {
      "type": "string",
      "title": "Label",
      "description": "A label for this Parser Stage",
      "maxLength": 255
    },
    "enabled": {
      "type": "boolean",
      "title": "Enable this Parser Stage",
      "default": true
    },
    "mediaTypes": {
      "type": "array",
      "title": "Media Types to match",
      "description": "Documents with a media type on this list will be matched by this parser stage. See inheritMediaTypes / use default media types for more.",
      "items": {
        "type": "string",
        "pattern": "^[^\\/]+\\/[^\\/]+$",
        "format": "rfc2646"
      }
    },
    "inheritMediaTypes": {
      "type": "boolean",
      "title": "Match default media types in this Parser Stage",
      "description": "Each parser stage has a built-in list of media types it handles by default. If this setting is true, that list will be used along with any optional additional types provided in the mediaTypes list. If this setting is false, this stage will only be selected for media types in the mediaTypes list, and the mediaTypes list becomes a mandatory property which must have at least one valid media type.",
      "default": true
    },
    "pathPatterns": {
      "type": "array",
      "title": "File names to parse",
      "description": "Specify a file name or pattern that must be matched for this parser stage to run. Forward slashes (\"/\") are used to join names of files inside archives with the archive name.",
      "items": {
        "type": "object",
        "properties": {
          "syntax": {
            "type": "string",
            "title": "Pattern type",
            "description": "glob uses bash shell-style wildcards; regex uses Java (PCRE-style) regex",
            "enum": ["glob", "regex"],
            "default": "glob"
          },
          "pattern": {
            "type": "string",
            "title": "File name or pattern",
            "description": "e.g.: \"z.txt\" or \"*.md\" or \"/a/*/b/f.txt\" for glob; \"z.txt$\" or \".*\\.txt$\" or \"^/a/[^\\/]*/b/f.txt$\" for regex"
          }
        }
      }
    },
    "errorHandling": {
      "type": "string",
      "title": "Error Handling",
      "enum": ["ignore", "log", "fail", "mark"],
      "default": "mark"
    },
    "outputFieldPrefix": {
      "type": "string",
      "title": "Prefix parsed fields with",
      "description": "Fields extracted by this parser will be prefixed with this string. The remainder of the field name will be as detected in the stream",
      "maxLength": 20,
      "pattern": "^$|^[A-Za-z_][A-Za-z0-9_\\-\\.]+$"
    },
    "metadataOnly": {
      "type": "boolean",
      "title": "Only parse metadata",
      "default": false
    },
    "maxBytesToKeep": {
      "type": "integer",
      "title": "Maximum bytes to keep",
      "default": 1048576
    },
    "type": {
      "type": "string",
      "enum": ["fallback"],
      "default": "fallback"
    }
  },
  "additionalProperties": false,
  "category": "Other",
  "categoryPriority": 1,
  "unsafe": false
};

export const SchemaParamFields = ({schema}) => {
  const sanitize = str => {
    if (typeof str !== "string") return str;
    return str.replace(/^"(.*)"$/s, "$1").replace(/\\/g, "").replace(/"/g, "'");
  };
  const formatDescription = str => {
    const s = sanitize(str);
    return (/[.!?]\)*$/).test(s) ? s : `${s}.`;
  };
  const {description, properties = {}, required: requiredProps = []} = schema;
  const visibleProps = useMemo(() => Object.entries(properties).filter(([, prop]) => !prop.hints?.includes("hidden")), [properties]);
  return <div>
      {description && <p>{formatDescription(description)}</p>}

      {visibleProps.map(([name, prop]) => {
    const isRequired = requiredProps.includes(name);
    const hasDefault = prop.default !== undefined;
    const rawDefault = prop.default;
    const isComplexDefault = hasDefault && (typeof rawDefault === "object" || typeof rawDefault === "string" && (rawDefault.length > 20 || rawDefault.includes('"')));
    const fieldProps = {
      key: name,
      body: prop.title || name,
      type: prop.type,
      ...prop.title && ({
        post: [<><span className="text-stone-400 dark:text-stone-500">API property: </span>{name}</>]
      }),
      ...isRequired && ({
        required: true
      }),
      ...!isComplexDefault && hasDefault ? {
        default: sanitize(String(rawDefault))
      } : {}
    };
    const isObject = prop.type === "object" && prop.properties;
    const isArrayOfObjects = prop.type === "array" && prop.items?.type === "object" && prop.items.properties;
    return <ParamField {...fieldProps}>
            {prop.description && <p>{formatDescription(prop.description)}</p>}

            {isComplexDefault && <div className="flex">
                <p>
                  <strong>Default:</strong>
                </p>
                <pre className="!my-0">
                  <code>
                    {JSON.stringify(rawDefault, null, 2)}
                  </code>
                </pre>
              </div>}

            {isArrayOfObjects && <div className="flex">
              <p>
                <strong>Object attributes:</strong>
              </p>
              <pre className="!my-0">
                <code>
                  {'{\n'}
                  {Object.entries(prop.items.properties).map(([iname, iprop]) => <>
                      {`  ${iname}`}
                      {prop.items?.required?.includes(iname) && <span style={{
      color: 'red'
    }}> required</span>}
                      {`: {\n    display name: ${sanitize(iprop.title || '')}\n    type: ${iprop.type}\n  }\n`}
                    </>)}
                  {'}'}
                </code>
              </pre>
              </div>}

            {isObject && <Expandable title="properties">
                <SchemaParamFields schema={{
      properties: prop.properties,
      required: prop.required
    }} />
              </Expandable>}
          </ParamField>;
  })}
    </div>;
};

export const LwTemplate = ({title = "Key questions to get you started", icon = "sparkles", cta = "Powered by Agent Studio", linkHref = "https://lucidworks.com/demo/?utm_source=docs&utm_medium=referral&utm_campaign=docs_cta_ai"}) => {
  const [isLoaded, setIsLoaded] = useState(false);
  useEffect(() => {
    const timer = setTimeout(() => {
      setIsLoaded(true);
    }, 500);
    return () => clearTimeout(timer);
  }, []);
  return <div className="lw-template-container">
      <Card title={title} icon={icon}>
        {isLoaded && <span dangerouslySetInnerHTML={{
    __html: `<lw-template id="a029c1a9-28be-427e-b0e1-5d918920246a"></lw-template
            >`
  }} />}
        <Link href={linkHref} className="agent-studio-link text-left text-gray-600 gap-2 dark:text-gray-400 text-sm font-medium flex flex-row items-center hover:text-primary dark:hover:text-primary-light group-hover:text-primary group-hover:dark:text-primary-light">Powered by Lucidworks Agent Studio</Link>
      </Card>
    </div>;
};

[localhost link]: http://localhost:3000/docs/4/fusion-server/reference/parser-stages/fallback-parser

[mintlify link]: https://doc.lucidworks.com/docs/4/fusion-server/reference/parser-stages/fallback-parser

[old doc.lw link]: https://doc.lucidworks.com/fusion/5.9/378

The Fallback parser stage is useful for processing data that Fusion does not have a specified parsing process for. Fallback does not technically parse data, since it does not know what to do with it, it simply copies the raw bytes into a Solr document. If your Fusion parser stage configuration encounters data it does not know how to parse, such as someone’s proprietary data file format, it will copy it as-is, whereas if it encounters recognizable data in more common file types, such as PDFs, Fusion will parse the text and metadata using Tika.

<LwTemplate />

The Fallback parser acts as the final stage that attempts to parse any documents that haven’t been parsed already. More commonly, the parser selects a stage specifically built to handle the data and runs that stage.

<Tip>
  When entering configuration values in the UI, use *unescaped* characters, such as `\t` for the tab character. When entering configuration values in the API, use *escaped* characters, such as `\\t` for the tab character.
</Tip>

<SchemaParamFields schema={schema} />