docs: DOC-1139: Add HTML import/export documentation for Groovy

docs/groovy/how-to-guides/data-import-export/html-export.md

@@ -0,0 +1,33 @@
+---
+title: Export HTML files
+---
+
+Deephaven can convert tables to HTML table-formatted strings via the [`html`](/core/javadoc/io/deephaven/engine/util/TableTools.html#html(io.deephaven.engine.table.Table)) method from [`TableTools`](/core/javadoc/io/deephaven/engine/util/TableTools.html). It converts a Deephaven table to a string HTML table.
+
+## `html`
+
+The [`html`](/core/javadoc/io/deephaven/engine/util/TableTools.html#html(io.deephaven.engine.table.Table)) method requires only a single argument — the table to convert. Here, we'll create a simple table and convert it to HTML.
+
+```groovy order=:log,table
+table = newTable(
+    stringCol("Letter", "A", "B", "C"),
+    intCol("Num", 1, 2, 3),
+    instantCol("Datetime",
+        parseInstant("2007-12-03T10:15:30.00Z"),
+        parseInstant("2007-12-03T10:15:30.00Z"),
+        parseInstant("2007-12-03T10:15:30.00Z"),
+    )
+)
+
+htmlTable = html(table)
+
+println(htmlTable)
+```
+
+> [!NOTE]
+> Since HTML tables represent all data as plain, untyped text, all typing will be lost.
+
+## Related documentation
+
+- [Read HTML files](./html-import.md)
+- [Export CSV files](./csv-export.md)

docs/groovy/how-to-guides/data-import-export/html-import.md

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+---
+title: Read HTML files into Deephaven tables
+---
+
+Deephaven does not provide built-in methods for reading HTML tables in Groovy. Because Groovy runs on the JVM, you can use any Java HTML parsing library to pull data from HTML into Deephaven tables.
+
+[Jsoup](https://jsoup.org/) is a popular Java library for parsing HTML, similar to [BeautifulSoup](https://www.crummy.com/software/BeautifulSoup/bs4/doc/) in Python. It handles malformed real-world HTML gracefully and bundles both HTTP fetching and HTML parsing in a single dependency. It is not included in Deephaven by default and must be added to the classpath before use. See [Install and use Java packages](../install-and-use-java-packages.md) for instructions on how to add external JARs to a Deephaven worker.
+
+Once Jsoup is available, you can use it in Groovy scripts to fetch and parse HTML tables, then construct Deephaven tables from the extracted data using [`newTable`](/core/javadoc/io/deephaven/engine/util/TableTools.html#newTable(io.deephaven.engine.table.impl.util.ColumnHolder...)) and column factory methods such as `stringCol`.
+
+## Related documentation
+
+- [Export HTML files](./html-export.md)
+- [Install and use Java packages](../install-and-use-java-packages.md)

docs/groovy/sidebar.json

@@ -181,6 +181,19 @@
                   }
                 ]
               },
+              {
+                "label": "HTML",
+                "items": [
+                  {
+                    "label": "Read HTML files",
+                    "path": "how-to-guides/data-import-export/html-import.md"
+                  },
+                  {
+                    "label": "Export HTML files",
+                    "path": "how-to-guides/data-import-export/html-export.md"
+                  }
+                ]
+              },
               {
                 "label": "Arrow Flight",
                 "path": "how-to-guides/data-import-export/arrow-flight.md"

docs/groovy/snapshots/d7689d421bd15c81dd8983f1c9027434.json

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+{"file":"how-to-guides/data-import-export/html-export.md","objects":{"table":{"type":"Table","data":{"columns":[{"name":"Letter","type":"java.lang.String"},{"name":"Num","type":"int"},{"name":"Datetime","type":"java.time.Instant"}],"rows":[[{"value":"A"},{"value":"1"},{"value":"2007-12-03 05:15:30.000"}],[{"value":"B"},{"value":"2"},{"value":"2007-12-03 05:15:30.000"}],[{"value":"C"},{"value":"3"},{"value":"2007-12-03 05:15:30.000"}]]}},":log":{"type":"Log","data":"<table border=\"1\">\n<tr>\n<th>Letter</th>\n<th>Num</th>\n<th>Datetime</th>\n</tr>\n<tr><td>A</td><td>1</td><td>2007-12-03T10:15:30.000000000 Etc/UTC</td></tr>\n<tr><td>B</td><td>2</td><td>2007-12-03T10:15:30.000000000 Etc/UTC</td></tr>\n<tr><td>C</td><td>3</td><td>2007-12-03T10:15:30.000000000 Etc/UTC</td></tr>\n</table>\n\n"}}}