jEdit is a programmer's text editor suited to Haxe development without an IDE. It performs syntax highlighting, but it needs a syntax file (called an edit mode in jEdit) to help it. You can use the JavaScript or ActionScript modes successfully, but it is better to tailor a file specifically.

Refer to the documentation of jEdit for how to install a new edit mode. In current jEdit versions, you have to save the mode below in a XML file (preferably named Haxe.xml) in jEdit's editing modes directory (this depends on your operating system, but usually it is jEdit's installation directory under Windows and /usr/share/jedit/modes under Linux if you have installed jEdit using a package manager). You also need to put a new entry in the catalog file which is placed at the same directory as the edit mode files. The catalog entry should be

<MODE NAME="Haxe"        FILE="Haxe.xml"
                FILE_NAME_GLOB="*.hx" />

To make the new edit mode work you can restart jEdit or select Reload Edit Modes from the Troubleshooting submenu of the Utilities menu.

The following will work as the contents of a mode file Haxe.xml.

<?xml version="1.0"?>
<!DOCTYPE MODE SYSTEM "xmode.dtd">

<!--
  This mode highlights the syntax of Haxe, but unlike most modes,
  it does not attempt to highlight standard API, except those core
  types defined prior to any imports, e.g. the Bool class.
-->
<MODE>
  <PROPS>
    <PROPERTY NAME="indentOpenBrackets" VALUE="{" />
    <PROPERTY NAME="indentCloseBrackets" VALUE="}" />
    <!-- the ; hack is there so that stuff like if(bob) fred();
         does not indent the next line -->
    <PROPERTY NAME="indentPrevLine"
      VALUE="\s*(if|while)\s*(|else|case|default:)[^;]*|for\s*\(.*)" />
    <!-- set this to 'true' if you want to use GNU coding style -->
    <PROPERTY NAME="doubleBracketIndent" VALUE="false" />
    <PROPERTY NAME="lineUpClosingBracket" VALUE="true" />
    <PROPERTY NAME="commentStart" VALUE="/*" />
    <PROPERTY NAME="commentEnd" VALUE="*/" />
    <PROPERTY NAME="lineComment" VALUE="//" />
    <PROPERTY NAME="wordBreakChars" VALUE="+-.,=&lt;&gt;/?^&amp;*" />
  </PROPS>

  <RULES ESCAPE="\\"
         IGNORE_CASE="FALSE" HIGHLIGHT_DIGITS="TRUE"
         DIGIT_RE="(0x[[:xdigit:]]+|[[:digit:]]+((E|e|)[[:digit:]]*)?)">
    <!-- whitespace: (space and tab) -->
    <SPAN TYPE="COMMENT1">
      <BEGIN>/*</BEGIN>
      <END>*/</END>
    </SPAN>

    <SPAN TYPE="LITERAL1" NO_LINE_BREAK="TRUE">
      <BEGIN>"</BEGIN>
      <END>"</END>
    </SPAN>

    <SPAN TYPE="LITERAL1" NO_LINE_BREAK="TRUE">
      <BEGIN>'</BEGIN>
      <END>'</END>
    </SPAN>

    <!-- Mark anything preceding ( as a function. -->
    <MARK_PREVIOUS TYPE="FUNCTION" EXCLUDE_MATCH="TRUE">(</MARK_PREVIOUS>
    <!-- Sometimes I leave a space. -->
    <MARK_PREVIOUS TYPE="FUNCTION" EXCLUDE_MATCH="TRUE"> (</MARK_PREVIOUS>

    <EOL_SPAN TYPE="COMMENT1">//</EOL_SPAN>
                
    <!-- Make preprocessor directive look like comment 3 -->
    <EOL_SPAN TYPE="COMMENT3">#</EOL_SPAN>

    <!-- Regular expression highlighting -->
    <SEQ_REGEXP TYPE="MARKUP"
                HASH_CHAR="~"
                AT_WORD_START="TRUE"
    >~([[:punct:]])(?:.*?[^\\])*?\1[sgiexom]*</SEQ_REGEXP>
                
    <SEQ TYPE="NULL">)</SEQ>
    <SEQ TYPE="NULL">(</SEQ>

    <SEQ TYPE="OPERATOR">=</SEQ>
    <SEQ TYPE="OPERATOR">!</SEQ>
    <SEQ TYPE="OPERATOR">+</SEQ>
    <SEQ TYPE="OPERATOR">-</SEQ>
    <SEQ TYPE="OPERATOR">/</SEQ>
    <SEQ TYPE="OPERATOR">*</SEQ>
    <SEQ TYPE="OPERATOR">&gt;</SEQ>
    <SEQ TYPE="OPERATOR">&lt;</SEQ>
    <SEQ TYPE="OPERATOR">%</SEQ>
    <SEQ TYPE="OPERATOR">&amp;</SEQ>
    <SEQ TYPE="OPERATOR">|</SEQ>
    <SEQ TYPE="OPERATOR">^</SEQ>
    <SEQ TYPE="OPERATOR">~</SEQ>
    <SEQ TYPE="OPERATOR">.</SEQ>
    <SEQ TYPE="OPERATOR">}</SEQ>
    <SEQ TYPE="OPERATOR">{</SEQ>
    <SEQ TYPE="OPERATOR">,</SEQ>
    <SEQ TYPE="OPERATOR">;</SEQ>
    <SEQ TYPE="OPERATOR">]</SEQ>
    <SEQ TYPE="OPERATOR">[</SEQ>
    <SEQ TYPE="OPERATOR">?</SEQ>
    <SEQ TYPE="OPERATOR">:</SEQ>
                
    <KEYWORDS IGNORE_CASE="FALSE">
                
      <!-- Haxe's flow control words -->
      <KEYWORD1>break</KEYWORD1>
      <KEYWORD1>case</KEYWORD1>
      <KEYWORD1>catch</KEYWORD1>
      <KEYWORD1>continue</KEYWORD1>
      <KEYWORD1>default</KEYWORD1>
      <KEYWORD1>do</KEYWORD1>
      <KEYWORD1>else</KEYWORD1>
      <KEYWORD1>for</KEYWORD1>
      <KEYWORD1>if</KEYWORD1>
      <KEYWORD1>in</KEYWORD1>
      <KEYWORD1>return</KEYWORD1>
      <KEYWORD1>switch</KEYWORD1>
      <KEYWORD1>throw</KEYWORD1>
      <KEYWORD1>try</KEYWORD1>
      <KEYWORD1>while</KEYWORD1>

      <!-- Haxe's declarative words -->
      <KEYWORD2>class</KEYWORD2>
      <KEYWORD2>enum</KEYWORD2>
      <KEYWORD2>extends</KEYWORD2>
      <KEYWORD2>extern</KEYWORD2>
      <KEYWORD2>function</KEYWORD2>
      <KEYWORD2>implements</KEYWORD2>
      <KEYWORD2>import</KEYWORD2>
      <KEYWORD2>interface</KEYWORD2>
      <KEYWORD2>inline</KEYWORD2>
      <KEYWORD2>override</KEYWORD2>
      <KEYWORD2>package</KEYWORD2>
      <KEYWORD2>private</KEYWORD2>
      <KEYWORD2>public</KEYWORD2>
      <KEYWORD2>static</KEYWORD2>
      <KEYWORD2>typedef</KEYWORD2>
      <KEYWORD2>var</KEYWORD2>

      <!-- Built-in types -->
      <KEYWORD3>ArrayAccess</KEYWORD3>
      <KEYWORD3>Array</KEYWORD3>
      <KEYWORD3>Bool</KEYWORD3>
      <KEYWORD3>Dynamic</KEYWORD3>
      <KEYWORD3>Float</KEYWORD3>
      <KEYWORD3>Int</KEYWORD3>
      <KEYWORD3>Iterator</KEYWORD3>
      <KEYWORD3>Iterable</KEYWORD3>
      <KEYWORD3>Null</KEYWORD3>
      <KEYWORD3>Object</KEYWORD3>
      <KEYWORD3>String</KEYWORD3>
      <KEYWORD3>UInt</KEYWORD3>
      <KEYWORD3>Void</KEYWORD3>

      <!-- Special keywords -->
      <LITERAL2>cast</LITERAL2>
      <LITERAL2>new</LITERAL2>
      <LITERAL2>super</LITERAL2>
      <LITERAL2>this</LITERAL2>
      <LITERAL2>trace</LITERAL2>
      <LITERAL2>typeof</LITERAL2>
      <LITERAL2>untyped</LITERAL2>
      <!-- Literals -->
      <LITERAL2>false</LITERAL2>
      <LITERAL2>null</LITERAL2>
      <LITERAL2>true</LITERAL2>
      <LITERAL2>undefined</LITERAL2>
    </KEYWORDS>
  </RULES>
</MODE>