diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 0cc5da870..9f5814605 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -18,7 +18,7 @@ repos:
 #     hooks:
 #     -   id: black
 -   repo: https://github.com/astral-sh/ruff-pre-commit
-    rev: v0.7.3
+    rev: v0.8.0
     hooks:
     -   id: ruff
 # -   repo: https://github.com/econchick/interrogate
diff --git a/CHANGELOG.md b/CHANGELOG.md
index a8a97ff58..438a0c7df 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,7 +3,7 @@
 ## HDMF 4.0.0 (Upcoming)
 
 ### Deprecations
-- The following classes have been deprecated and removed: Array, AbstractSortedArray, SortedArray, LinSpace, Query, RegionSlicer, ListSlicer, H5RegionSlicer, DataRegion. The following methods have been deprecated and removed: fmt_docval_args, call_docval_func, get_container_cls, add_child, set_dataio (now refactored as set_data_io). We have also removed all early evelopment for region references. @mavaylon1 [#1998](https://github.com/hdmf-dev/hdmf/pull/1198)
+- The following classes have been deprecated and removed: Array, AbstractSortedArray, SortedArray, LinSpace, Query, RegionSlicer, ListSlicer, H5RegionSlicer, DataRegion, RegionBuilder. The following methods have been deprecated and removed: fmt_docval_args, call_docval_func, get_container_cls, add_child, set_dataio (now refactored as set_data_io). We have also removed all early development for region references. @mavaylon1, @rly [#1998](https://github.com/hdmf-dev/hdmf/pull/1198), [#1212](https://github.com/hdmf-dev/hdmf/pull/1212)
 - Python 3.8 has been deprecated. Python 3.9 is the new minimum with support for Python 3.13. @mavaylon1 [#1209](https://github.com/hdmf-dev/hdmf/pull/1209)
 
 ### Enhancements
diff --git a/docs/source/conf.py b/docs/source/conf.py
index c20869e12..d385630d2 100644
--- a/docs/source/conf.py
+++ b/docs/source/conf.py
@@ -87,7 +87,6 @@
 
 nitpicky = True
 nitpick_ignore = [('py:class', 'Intracomm'),
-                  ('py:class', 'h5py.RegionReference'),
                   ('py:class', 'h5py._hl.dataset.Dataset'),
                   ('py:class', 'function'),
                   ('py:class', 'unittest.case.TestCase'),
diff --git a/docs/source/overview_software_architecture.rst b/docs/source/overview_software_architecture.rst
index 973a01b2f..d63c953fe 100644
--- a/docs/source/overview_software_architecture.rst
+++ b/docs/source/overview_software_architecture.rst
@@ -68,7 +68,7 @@ Builder
    * :py:class:`~hdmf.build.builders.GroupBuilder` - represents a collection of objects
    * :py:class:`~hdmf.build.builders.DatasetBuilder` - represents data
    * :py:class:`~hdmf.build.builders.LinkBuilder` - represents soft-links
-   * :py:class:`~hdmf.build.builders.RegionBuilder` - represents a slice into data (Subclass of :py:class:`~hdmf.build.builders.DatasetBuilder`)
+   * :py:class:`~hdmf.build.builders.ReferenceBuilder` - represents a reference to another group or dataset
 
 * **Main Module:** :py:class:`hdmf.build.builders`
 
diff --git a/src/hdmf/backends/hdf5/h5tools.py b/src/hdmf/backends/hdf5/h5tools.py
index bf8f86bb9..d30cef06c 100644
--- a/src/hdmf/backends/hdf5/h5tools.py
+++ b/src/hdmf/backends/hdf5/h5tools.py
@@ -908,8 +908,6 @@ def get_type(cls, data):
         "utf-8": H5_TEXT,
         "ascii": H5_BINARY,
         "bytes": H5_BINARY,
-        "ref": H5_REF,
-        "reference": H5_REF,
         "object": H5_REF,
         "isodatetime": H5_TEXT,
         "datetime": H5_TEXT,
@@ -1492,7 +1490,7 @@ def __is_ref(self, dtype):
         if isinstance(dtype, dict):  # may be dict from reading a compound dataset
             return self.__is_ref(dtype['dtype'])
         if isinstance(dtype, str):
-            return dtype == DatasetBuilder.OBJECT_REF_TYPE or dtype == DatasetBuilder.REGION_REF_TYPE
+            return dtype == DatasetBuilder.OBJECT_REF_TYPE
         return False
 
     def __queue_ref(self, func):
@@ -1541,7 +1539,7 @@ def generate_dataset_html(dataset):
 
         array_info_dict = get_basic_array_info(dataset)
         if isinstance(dataset, h5py.Dataset):
-
+            dataset_type = "HDF5 dataset"
             # get info from hdf5 dataset
             compressed_size = dataset.id.get_storage_size()
             if hasattr(dataset, "nbytes"):  # TODO: Remove this after h5py minimal version is larger than 3.0
@@ -1556,10 +1554,13 @@ def generate_dataset_html(dataset):
                             "Compression opts": dataset.compression_opts,
                             "Compression ratio": compression_ratio,
                             }
-
             array_info_dict.update(hdf5_info_dict)
 
-        # generate html repr
-        repr_html = generate_array_html_repr(array_info_dict, dataset, "HDF5 dataset")
+        elif isinstance(dataset, np.ndarray):
+            dataset_type = "NumPy array"
+        else:
+            dataset_type = dataset.__class__.__name__
+
+        repr_html = generate_array_html_repr(array_info_dict, dataset, dataset_type)
 
         return repr_html
diff --git a/src/hdmf/build/__init__.py b/src/hdmf/build/__init__.py
index ea5d21152..87e0ac57e 100644
--- a/src/hdmf/build/__init__.py
+++ b/src/hdmf/build/__init__.py
@@ -1,4 +1,4 @@
-from .builders import Builder, DatasetBuilder, GroupBuilder, LinkBuilder, ReferenceBuilder, RegionBuilder
+from .builders import Builder, DatasetBuilder, GroupBuilder, LinkBuilder, ReferenceBuilder
 from .classgenerator import CustomClassGenerator, MCIClassGenerator
 from .errors import (BuildError, OrphanContainerBuildError, ReferenceTargetNotBuiltError, ContainerConfigurationError,
                      ConstructError)
diff --git a/src/hdmf/build/builders.py b/src/hdmf/build/builders.py
index cb658b6d4..2d90c24e3 100644
--- a/src/hdmf/build/builders.py
+++ b/src/hdmf/build/builders.py
@@ -6,7 +6,6 @@
 from datetime import datetime, date
 
 import numpy as np
-from h5py import RegionReference
 
 from ..utils import docval, getargs, get_docval
 
@@ -320,11 +319,10 @@ def values(self):
 
 class DatasetBuilder(BaseBuilder):
     OBJECT_REF_TYPE = 'object'
-    REGION_REF_TYPE = 'region'
 
     @docval({'name': 'name', 'type': str, 'doc': 'The name of the dataset.'},
             {'name': 'data',
-             'type': ('array_data', 'scalar_data', 'data', 'DatasetBuilder', 'RegionBuilder', Iterable, datetime, date),
+             'type': ('array_data', 'scalar_data', 'data', 'DatasetBuilder', Iterable, datetime, date),
              'doc': 'The data in this dataset.', 'default': None},
             {'name': 'dtype', 'type': (type, np.dtype, str, list),
              'doc': 'The datatype of this dataset.', 'default': None},
@@ -429,20 +427,3 @@ def __init__(self, **kwargs):
     def builder(self):
         """The target builder object."""
         return self['builder']
-
-
-class RegionBuilder(ReferenceBuilder):
-
-    @docval({'name': 'region', 'type': (slice, tuple, list, RegionReference),
-             'doc': 'The region, i.e. slice or indices, into the target dataset.'},
-            {'name': 'builder', 'type': DatasetBuilder, 'doc': 'The dataset this region reference applies to.'})
-    def __init__(self, **kwargs):
-        """Create a builder object for a region reference."""
-        region, builder = getargs('region', 'builder', kwargs)
-        super().__init__(builder)
-        self['region'] = region
-
-    @property
-    def region(self):
-        """The selected region of the target dataset."""
-        return self['region']
diff --git a/src/hdmf/build/objectmapper.py b/src/hdmf/build/objectmapper.py
index c2ef44b5f..176de322c 100644
--- a/src/hdmf/build/objectmapper.py
+++ b/src/hdmf/build/objectmapper.py
@@ -6,7 +6,7 @@
 
 import numpy as np
 
-from .builders import DatasetBuilder, GroupBuilder, LinkBuilder, Builder, ReferenceBuilder, RegionBuilder, BaseBuilder
+from .builders import DatasetBuilder, GroupBuilder, LinkBuilder, Builder, ReferenceBuilder, BaseBuilder
 from .errors import (BuildError, OrphanContainerBuildError, ReferenceTargetNotBuiltError, ContainerConfigurationError,
                      ConstructError)
 from .manager import Proxy, BuildManager
@@ -1214,8 +1214,6 @@ def __get_subspec_values(self, builder, spec, manager):
                 continue
             if isinstance(attr_val, (GroupBuilder, DatasetBuilder)):
                 ret[attr_spec] = manager.construct(attr_val)
-            elif isinstance(attr_val, RegionBuilder):  # pragma: no cover
-                raise ValueError("RegionReferences as attributes is not yet supported")
             elif isinstance(attr_val, ReferenceBuilder):
                 ret[attr_spec] = manager.construct(attr_val.builder)
             else:
diff --git a/src/hdmf/container.py b/src/hdmf/container.py
index 864b34ee9..ce4e8b821 100644
--- a/src/hdmf/container.py
+++ b/src/hdmf/container.py
@@ -707,8 +707,11 @@ def _generate_field_html(self, key, value, level, access_code):
             return f'<div style="margin-left: {level * 20}px;" class="container-fields"><span class="field-key"' \
                    f' title="{access_code}">{key}: </span><span class="field-value">{value}</span></div>'
 
-        is_array_data = isinstance(value, (np.ndarray, h5py.Dataset, DataIO)) or \
-            (hasattr(value, "store") and hasattr(value, "shape"))  # Duck typing for zarr array
+        # Detects array-like objects that conform to the Array Interface specification
+        # (e.g., NumPy arrays, HDF5 datasets, DataIO objects). Objects must have both
+        # 'shape' and 'dtype' attributes. Iterators are excluded as they lack 'shape'.
+        # This approach keeps the implementation generic without coupling to specific backends methods
+        is_array_data = hasattr(value, "shape") and hasattr(value, "dtype")
 
         if is_array_data:
             html_content = self._generate_array_html(value, level + 1)
@@ -735,14 +738,29 @@ def _generate_field_html(self, key, value, level, access_code):
 
 
     def _generate_array_html(self, array, level):
-        """Generates HTML for array data"""
+        """Generates HTML for array data (e.g., NumPy arrays, HDF5 datasets, Zarr datasets and DataIO objects)."""
 
-        read_io = self.get_read_io()  # if the Container was read from file, get IO object
-        if read_io is not None: # Note that sometimes numpy array have a read_io attribute
-            repr_html = read_io.generate_dataset_html(array)
-        else:
+        is_numpy_array = isinstance(array, np.ndarray)
+        read_io = self.get_read_io()
+        it_was_read_with_io = read_io is not None
+        is_data_io = isinstance(array, DataIO)
+
+        if is_numpy_array:
             array_info_dict = get_basic_array_info(array)
             repr_html = generate_array_html_repr(array_info_dict, array, "NumPy array")
+        elif is_data_io:
+            array_info_dict = get_basic_array_info(array.data)
+            repr_html = generate_array_html_repr(array_info_dict, array.data, "DataIO")
+        elif it_was_read_with_io:
+            # The backend handles the representation here. Two special cases worth noting:
+            # 1. Array-type attributes (e.g., start_frame in ImageSeries) remain NumPy arrays
+            #    even when their parent container has an IO
+            # 2. Data may have been modified after being read from storage
+            repr_html = read_io.generate_dataset_html(array)
+        else:  # Not sure which object could get here
+            object_class = array.__class__.__name__
+            array_info_dict = get_basic_array_info(array.data)
+            repr_html = generate_array_html_repr(array_info_dict, array.data, object_class)
 
         return f'<div style="margin-left: {level * 20}px;" class="container-fields">{repr_html}</div>'
 
diff --git a/src/hdmf/spec/spec.py b/src/hdmf/spec/spec.py
index e10d5e43e..d5adf6b5e 100644
--- a/src/hdmf/spec/spec.py
+++ b/src/hdmf/spec/spec.py
@@ -38,7 +38,6 @@ class DtypeHelper:
         'uint32': ["uint32", "uint"],
         'uint64': ["uint64"],
         'object': ['object'],
-        'region': ['region'],
         'numeric': ['numeric'],
         'isodatetime': ["isodatetime", "datetime", "date"]
     }
@@ -174,12 +173,13 @@ def path(self):
 
 _ref_args = [
     {'name': _target_type_key, 'type': str, 'doc': 'the target type GroupSpec or DatasetSpec'},
-    {'name': 'reftype', 'type': str, 'doc': 'the type of references this is i.e. region or object'},
+    {'name': 'reftype', 'type': str,
+     'doc': 'the type of reference this is. only "object" is supported currently.'},
 ]
 
 
 class RefSpec(ConstructableDict):
-    __allowable_types = ('object', 'region')
+    __allowable_types = ('object', )
 
     @docval(*_ref_args)
     def __init__(self, **kwargs):
@@ -200,10 +200,6 @@ def reftype(self):
         '''The type of reference'''
         return self['reftype']
 
-    @docval(rtype=bool, returns='True if this RefSpec specifies a region reference, False otherwise')
-    def is_region(self):
-        return self['reftype'] == 'region'
-
 
 _attr_args = [
     {'name': 'name', 'type': str, 'doc': 'The name of this attribute'},
diff --git a/src/hdmf/utils.py b/src/hdmf/utils.py
index 6b5900384..c21382a2a 100644
--- a/src/hdmf/utils.py
+++ b/src/hdmf/utils.py
@@ -894,7 +894,7 @@ def convert_bytes_to_str(bytes_size):
 
     return basic_array_info_dict
 
-def generate_array_html_repr(backend_info_dict, array, dataset_type=None):
+def generate_array_html_repr(array_info_dict, array, dataset_type=None):
     def html_table(item_dicts) -> str:
         """
         Generates an html table from a dictionary
@@ -912,14 +912,22 @@ def html_table(item_dicts) -> str:
         report += "</table>"
         return report
 
-    array_info_html = html_table(backend_info_dict)
+    array_info_html = html_table(array_info_dict)
     repr_html = dataset_type + "<br>" + array_info_html if dataset_type is not None else array_info_html
 
-    if hasattr(array, "nbytes"):  # TODO: Remove this after h5py minimal version is larger than 3.0
-        array_size = array.nbytes
+    # Array like might lack nbytes (h5py < 3.0) or size (DataIO object)
+    if hasattr(array, "nbytes"):
+        array_size_bytes = array.nbytes
     else:
-        array_size = array.size * array.dtype.itemsize
-    array_is_small = array_size < 1024 * 0.1 # 10 % a kilobyte to display the array
+        if hasattr(array, "size"):
+            array_size = array.size
+        else:
+            import math
+            array_size = math.prod(array.shape)
+        array_size_bytes = array_size * array.dtype.itemsize
+
+    # Heuristic for displaying data
+    array_is_small = array_size_bytes < 1024 * 0.1 # 10 % a kilobyte to display the array
     if array_is_small:
         repr_html += "<br>" + str(np.asarray(array))
 
diff --git a/src/hdmf/validate/validator.py b/src/hdmf/validate/validator.py
index daa5adac4..d7ec78eaa 100644
--- a/src/hdmf/validate/validator.py
+++ b/src/hdmf/validate/validator.py
@@ -8,7 +8,7 @@
 
 from .errors import Error, DtypeError, MissingError, MissingDataType, ShapeError, IllegalLinkError, IncorrectDataType
 from .errors import ExpectedArrayError, IncorrectQuantityError
-from ..build import GroupBuilder, DatasetBuilder, LinkBuilder, ReferenceBuilder, RegionBuilder
+from ..build import GroupBuilder, DatasetBuilder, LinkBuilder, ReferenceBuilder
 from ..build.builders import BaseBuilder
 from ..spec import Spec, AttributeSpec, GroupSpec, DatasetSpec, RefSpec, LinkSpec
 from ..spec import SpecNamespace
@@ -124,9 +124,6 @@ def get_type(data, builder_dtype=None):
     # Bytes data
     elif isinstance(data, bytes):
         return 'ascii', get_string_format(data)
-    # RegionBuilder data
-    elif isinstance(data, RegionBuilder):
-        return 'region', None
     # ReferenceBuilder data
     elif isinstance(data, ReferenceBuilder):
         return 'object', None
diff --git a/tests/unit/build_tests/test_builder.py b/tests/unit/build_tests/test_builder.py
index a35dc64ac..62ebd0675 100644
--- a/tests/unit/build_tests/test_builder.py
+++ b/tests/unit/build_tests/test_builder.py
@@ -1,4 +1,4 @@
-from hdmf.build import GroupBuilder, DatasetBuilder, LinkBuilder, ReferenceBuilder, RegionBuilder
+from hdmf.build import GroupBuilder, DatasetBuilder, LinkBuilder, ReferenceBuilder
 from hdmf.testing import TestCase
 
 
@@ -392,12 +392,3 @@ def test_constructor(self):
         db = DatasetBuilder('db1', [1, 2, 3])
         rb = ReferenceBuilder(db)
         self.assertIs(rb.builder, db)
-
-
-class TestRegionBuilder(TestCase):
-
-    def test_constructor(self):
-        db = DatasetBuilder('db1', [1, 2, 3])
-        rb = RegionBuilder(slice(1, 3), db)
-        self.assertEqual(rb.region, slice(1, 3))
-        self.assertIs(rb.builder, db)
diff --git a/tests/unit/spec_tests/test_ref_spec.py b/tests/unit/spec_tests/test_ref_spec.py
index bb1c0efb8..3277673d1 100644
--- a/tests/unit/spec_tests/test_ref_spec.py
+++ b/tests/unit/spec_tests/test_ref_spec.py
@@ -15,9 +15,3 @@ def test_constructor(self):
     def test_wrong_reference_type(self):
         with self.assertRaises(ValueError):
             RefSpec('TimeSeries', 'unknownreftype')
-
-    def test_isregion(self):
-        spec = RefSpec('TimeSeries', 'object')
-        self.assertFalse(spec.is_region())
-        spec = RefSpec('Data', 'region')
-        self.assertTrue(spec.is_region())