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HTML strip character filter
The html_strip character filter removes HTML tags, such as <div>, <p>, and <a>, from the input text and renders plain text. The filter can be configured to preserve certain tags or decode specific HTML entities, such as , into spaces.
Example
The following request applies an html_strip character filter to the provided text:
GET /_analyze
{
"tokenizer": "keyword",
"char_filter": [
"html_strip"
],
"text": "<p>Commonly used calculus symbols include α, β and θ </p>"
}
The response contains the token in which HTML characters have been converted to their decoded values:
{
"tokens": [
{
"token": """
Commonly used calculus symbols include α, β and θ
""",
"start_offset": 0,
"end_offset": 74,
"type": "word",
"position": 0
}
]
}
Parameters
The html_strip character filter can be configured with the following parameter.
| Parameter | Required/Optional | Data type | Description |
|---|---|---|---|
escaped_tags | Optional | Array of strings | An array of HTML element names, specified without the enclosing angle brackets (< >). The filter does not remove elements in this list when stripping HTML from the text. For example, setting the array to ["b", "i"] will prevent the <b> and <i> elements from being stripped. |
Example: Custom analyzer with lowercase filter
The following example request creates a custom analyzer that strips HTML tags and converts the plain text to lowercase by using the html_strip analyzer and lowercase filter:
PUT /html_strip_and_lowercase_analyzer
{
"settings": {
"analysis": {
"char_filter": {
"html_filter": {
"type": "html_strip"
}
},
"analyzer": {
"html_strip_analyzer": {
"type": "custom",
"char_filter": ["html_filter"],
"tokenizer": "standard",
"filter": ["lowercase"]
}
}
}
}
}
Use the following request to examine the tokens generated using the analyzer:
GET /html_strip_and_lowercase_analyzer/_analyze
{
"analyzer": "html_strip_analyzer",
"text": "<h1>Welcome to <strong>OpenSearch</strong>!</h1>"
}
In the response, the HTML tags have been removed and the plain text has been converted to lowercase:
{
"tokens": [
{
"token": "welcome",
"start_offset": 4,
"end_offset": 11,
"type": "<ALPHANUM>",
"position": 0
},
{
"token": "to",
"start_offset": 12,
"end_offset": 14,
"type": "<ALPHANUM>",
"position": 1
},
{
"token": "opensearch",
"start_offset": 23,
"end_offset": 42,
"type": "<ALPHANUM>",
"position": 2
}
]
}
Example: Custom analyzer that preserves HTML tags
The following example request creates a custom analyzer that preserves HTML tags:
PUT /html_strip_preserve_analyzer
{
"settings": {
"analysis": {
"char_filter": {
"html_filter": {
"type": "html_strip",
"escaped_tags": ["b", "i"]
}
},
"analyzer": {
"html_strip_analyzer": {
"type": "custom",
"char_filter": ["html_filter"],
"tokenizer": "keyword"
}
}
}
}
}
Use the following request to examine the tokens generated using the analyzer:
GET /html_strip_preserve_analyzer/_analyze
{
"analyzer": "html_strip_analyzer",
"text": "<p>This is a <b>bold</b> and <i>italic</i> text.</p>"
}
In the response, the italic and bold tags have been retained, as specified in the custom analyzer request:
{
"tokens": [
{
"token": """
This is a <b>bold</b> and <i>italic</i> text.
""",
"start_offset": 0,
"end_offset": 52,
"type": "word",
"position": 0
}
]
}