The `ignore_malformed` option is supported by a few of our field types, mainly numerics and dates, to still accept the document when such fields hold malformed values. See https://www.elastic.co/guide/en/elasticsearch/reference/current/ignore-malformed.html. Also `ignore_malformed` is an index level setting that gets applied to all field types that support it. 

The boolean field type does not support `ignore_malformed` but it should, so that if a boolean field cannot be parsed as a boolean, the document can still be accepted.


server/src/main/java/org/elasticsearch/index/mapper/BooleanFieldMapper.java
}
                if (upperTerm != null) {
                    u = docValueForSearch(upperTerm);
                    if (includeUpper == false) {
                        l = Math.min(0, l - 1);
                    }
                }
                if (l > u) {
                    return new MatchNoDocsQuery();
                }
                return SortedNumericDocValuesField.newSlowRangeQuery(name(), l, u);
            }
        }
    }
    private final Boolean nullValue;
    private final boolean indexed;
    private final boolean hasDocValues;
    private final boolean stored;
    private final Script script;
    private final FieldValues<Boolean> scriptValues;
    private final ScriptCompiler scriptCompiler;
    private final Version indexCreatedVersion;
    protected BooleanFieldMapper(
        String simpleName,
        MappedFieldType mappedFieldType,
        MultiFields multiFields,
        CopyTo copyTo,
        Builder builder
    ) {
        super(simpleName, mappedFieldType, multiFields, copyTo, builder.script.get() != null, builder.onScriptError.getValue());